The purpose of this document is to provide guidance to industry on how to control Listeria monocytogenes (L. monocytogenes) in refrigerated or frozen ready-to-eat (RF-RTE) foods. Specifically, this document provides guidance on:

• The formulation of RF-RTE foods to prevent the growth of L. monocytogenes;
• Treatment of foods to destroy viable cells of L. monocytogenes;
• Controls on ingredients;
• Controls on storing RF-RTE foods;
• Controls on:
  • Employee hygiene;
  • Design, construction, and operation of your physical plant;
  • Design, construction and maintenance of equipment; and
  • Transportation.
• Sanitation controls and monitoring;
• Monitoring critical surfaces and areas to detect locations that harbor Listeria species or L. monocytogenes;
• Corrective actions to consider if you detect Listeria species or L. monocytogenes on critical surfaces or areas or in food;
• Recommended training;
• Methods for collecting environmental samples;
• Methods for preparing environmental samples for analysis;
• Recommended methods to detect or enumerate Listeria species or L. monocytogenes;
• Recommended records of the controls that you establish and implement.

We recommend that you assess this guidance as it relates to each of your operations and tailor your control strategies to the specific circumstances of each operation.

FDA's guidance documents, including this guidance, do not establish legally enforceable responsibilities. Instead, guidance describes the Agency's current thinking on a topic and should be viewed only as recommendations, unless specific regulatory or statutory requirements are cited. The use of the word should in Agency guidance means that something is suggested or recommended, but not required.

L. monocytogenes is a bacterium that can contaminate foods and cause a mild non-invasive illness (called listerial gastroenteritis) or a severe, sometimes life-threatening, illness (called invasive listeriosis). Persons who have the greatest risk of experiencing listeriosis after consuming foods contaminated with L. monocytogenes are fetuses and neonates who are infected after the mother is exposed to L. monocytogenes during pregnancy, the elderly, and persons with weakened immune systems. Invasive listeriosis is characterized by a high case-fatality rate, ranging from 20 percent to 30 percent (Ref. 1).

L. monocytogenes is widespread in the environment. It is found in soil, water, sewage, and decaying vegetation. It can be readily isolated from humans, domestic animals, raw agricultural commodities, and food processing environments (particularly cool damp areas) (Refs. 2 through 4). Control of L. monocytogenes in the food processing environment has been the subject of a number of scientific publications (Refs. 5 through 10). L. monocytogenes can multiply slowly at refrigeration temperatures, thereby challenging an important defense against food-borne pathogens, refrigeration (Refs. 1, 11, and 12).

Most cases of human listeriosis occur sporadically - that is, in an isolated manner without any apparent pattern. However, much of what is known about the epidemiology of the disease has been derived from outbreak-associated cases, in which there is an abrupt increase in reports of the disease. With rare exceptions, foods that have been reported to be associated with outbreaks or sporadic cases of listeriosis have been foods that can support the growth of L. monocytogenes and that are ready-to-eat (including coleslaw, fresh soft cheese made with unpasteurized milk, frankfurters,⁽²⁾  deli meats, and butter) (Ref. 1). Outbreaks of listeriosis are often associated with a processing or production failure (Ref. 13); this association has been less evident among sporadic cases (Ref. 14).

In addition to this information obtained from reported cases of listeriosis, contamination data (largely obtained from samples of foods collected at retail or during storage before sale) are available in published scientific literature, government documents and industry documents, or were made available to us from unpublished government and industry documents (Ref. 1). These contamination data show that L. monocytogenes has been detected to varying degrees in unpasteurized and pasteurized milk, high fat dairy products, soft unripened cheese (cottage cheese, cream cheese, ricotta), cooked ready-to-eat crustaceans, smoked seafood, fresh soft cheese (queso fresco), semi-soft cheese (blue, brick, monterey), soft-ripened cheese (brie, camembert, feta), deli-type salads, sandwiches, fresh-cut fruits and vegetables, and raw molluscan shellfish (Ref. 1). However, these data also show that most RTE foods do not contain detectable numbers of L. monocytogenes. For many RTE foods, contamination of foods with L. monocytogenes can be avoided - e.g., through the application of current good manufacturing practices that establish controls on ingredients, listericidal and listeristatic processes, segregation of foods that have been cooked from those that have not, and sanitation. Sanitation controls include effective environmental monitoring programs designed to identify and eliminate L. monocytogenes in and on surfaces and areas in the plant.

In 1996, we published a paper entitled "U.S. position on Listeria monocytogenes in foods" (Ref. 15). In that paper, we described outbreaks of listeriosis and an active surveillance program for invasive listeriosis initiated by the Center for Disease Control and Prevention (CDC). In 2003, FDA and FSIS, in consultation with CDC, released a quantitative assessment (the Risk Assessment) (Ref. 1) of relative risk associated with consumption of certain categories of ready-to-eat foods that had a history of contamination with L. monocytogenes, or that were implicated epidemiologically with an outbreak or a sporadic case of listeriosis. The Risk Assessment estimated that the risk of listeriosis would vary widely among those food categories (Ref. 1).

The foods that the Risk Assessment estimated to pose the highest risk support the growth of L. monocytogenes. In contrast, the foods that the Risk Assessment estimated to pose the lowest risk of being associated with listeriosis are foods that have intrinsic or extrinsic factors to prevent the growth of L. monocytogenes, or that are processed to alter the normal characteristics of the food. ⁽³⁾ For example, it is well established (Refs. 12 and 16 through 18) that L. monocytogenes does not grow when:

• The pH of the food is less than or equal to 4.4;
• The water activity of the food is less than or equal to 0.92; or
• The food is frozen.

Foods may naturally have a pH or water activity that prevents growth of L. monocytogenes or may be deliberately processed to achieve those characteristics (e.g., by adding acid to deli-type salads to bring the pH to less than or equal to 4.4). Listeristatic control measures, such as antimicrobial substances, can prevent L. monocytogenes from growing in food (Ref. 12). Antimicrobial substances such as sorbic acid are commonly used to prevent the growth of L. monocytogenes in foods such as cheeses. Antimicrobial substances such as sorbic acid and benzoic acid are commonly used to prevent the growth of L. monocytogenes in foods such as deli-type salads. Naturally occurring or added antimicrobial substances can have an interactive or synergistic effect with other parameters of the formulation, such as pH, water activity, the presence of other preservatives, and processing temperature. A concept known as the "hurdle concept" states that several inhibitory factors (hurdles), while individually unable to inhibit microorganisms, will, nevertheless, be effective in combination (Refs 12 and 19). For reasons such as these, whether the addition of a particular anti-microbial substance to a particular food is effective in preventing the growth of L. monocytogenes is a case-by-case determination that can be demonstrated through scientific studies. A listeristatic control measure is generally considered to be effective if growth studies show less than a one log increase in the number of L. monocytogenes during replicate trials with the food of interest. For an example of how such studies are conducted, see Reference 20.

L. monocytogenes can survive longer under adverse environmental conditions than can many other vegetative bacteria that present a food safety concern. In addition to being able to survive and grow at refrigeration temperatures, L. monocytogenes tolerates high salt concentrations (such as in non-chlorinated brine chiller solutions) and survives frozen storage for extended periods. It is more resistant to nitrite and acidity than many other food-borne pathogens. It also is more resistant to heat than many other non-spore forming food-borne pathogens, although it can be killed by heating procedures such as those used to pasteurize milk ⁽⁴⁾ (Ref. 21).

Several scientific publications provide detailed recommendations for the control of L. monocytogenes in the food processing environment (see, e.g., Refs. 2 and 5 through 10). Many of the recommendations in this guidance are adapted from these published recommendations.

In the following tables, we list potential sources of L. monocytogenes and examples of scenarios that could lead to contamination of RF-RTE foods with L. monocytogenes.

Table 2 provides examples of scenarios that could lead to contamination of a RF-RTE food with L. monocytogenes (Refs. 5 and 9).

Table 2
Scenarios That Could Lead to Contamination with L. monocytogenes

• A packaging line is moved or modified significantly.
• Used equipment is brought from storage or another plant and installed into the process flow.
• An equipment breakdown occurs.
• Construction or major modifications are made to an area where RTE foods are processed or exposed (e.g., replacing refrigeration units or floors, replacing or building walls, modifications to sewer lines).
• A new employee, unfamiliar with the operation and L. monocytogenes controls, has been hired to work in, or to clean equipment in, the area where RTE foods are processed or exposed.
• Personnel who handle RTE foods touch surfaces or equipment likely to be contaminated (e.g., floor, trash cans) and do not change gloves or follow other required procedures before handling the food.
• Periods of heavy production make it difficult to clean the floors of holding coolers as scheduled.
• A drain backs up.
• Product is caught or hung-up on equipment. (Stagnant product in a system can be a major site of microbial growth during production.)
• Raw or under-processed foods are placed in an area designated for cooked foods.
• Frequent product changes on a packaging line cause you to change packaging film, labels, forming pockets or molds, line speeds, etc.
• Personnel are used interchangeably for packaging raw and cooked foods.
• Increased production causes you to perform wet cleaning of lines that have been taken down from production in the same room as lines that are running product.
• Heat exchangers have become compromised (e.g., with pinholes).
• Equipment parts, tubs, screens, etc. are cleaned on the floor.
• Waste bins in the RTE area are not properly maintained, cleaned and sanitized.
• Personnel handling RTE foods may come into contact with these items and then contaminate the foods and/or food contact surfaces.
• Re-circulating pumps and lines are not cleaned and sanitized.
• Indiscriminate use of high-pressure hoses in cleaning.
• Inappropriate use of footbaths in dry processing areas.
• Water is sprayed on wheels on transport cars when in-process product is stored near the wheels.

The Risk Assessment estimated that the risk of foodborne illness from consumption of RTE foods that do not support the growth of L. monocytogenes would be much lower than the risk from consumption of RTE foods that do support the growth of L. monocytogenes. Therefore, we provide recommendations on formulating RF-RTE foods so that they will not support the growth of L. monocytogenes.

Treatment of ingredients and in-process materials with a listericidal process can destroy viable cells of L. monocytogenes that enter a facility with new shipments of ingredients (such as raw seafood) or that are present in an unknown location on a food-contact surface or in an area that is in close proximity to a food-contact surface. Therefore, we provide recommendations on listericidal control measures that you could incorporate into your manufacturing process.

Raw foods (such as raw seafood, raw produce, and unpasteurized milk) are potential sources of contamination with L. monocytogenes. In addition, L. monocytogenes has been detected in a number of finished RF-RTE foods that could be purchased and used as an ingredient of other finished RF-RTE foods. Therefore, we provide recommendations on the control of ingredients used in RF-RTE foods.

The Risk Assessment discussed the effect of storage times and temperatures on the potential for viable cells of L. monocytogenes to increase in number. We provide recommendations on storage practices that are consistent with the discussion in the Risk Assessment.

The processing environment may be a primary source of L. monocytogenes (Refs. 2 and 5 through 10). Therefore, we provide recommendations on controls to reduce the potential for contamination of a RF-RTE food from:

• Personnel;
• The design, construction and operation of your plant;
• The design, construction and maintenance of equipment; and
• Sanitation controls

Because of its pervasiveness in the environment, L. monocytogenes may be introduced into your plant. Therefore, we provide recommendations on monitoring critical surfaces and areas in your plant for L. monocytogenes.

Likewise, contamination of a RF-RTE food with L. monocytogenes can occur during transportation, and viable cells of L. monocytogenes can grow if the temperature is not controlled during transportation. Therefore, we provide recommendations for controls on transportation.

Periodic sampling and testing of finished RF-RTE foods that you process can be an important reference for you to use in evaluating your control of L. monocytogenes over time. Therefore, we provide recommendations for such periodic sampling and testing. Although testing a single lot of finished product is not a practical means of assuring that the lot is free from contamination by L. monocytogenes, results from such testing, performed on many lots over a long period of time (many months to several years), can serve to document a baseline of performance and to validate the adequacy of other control measures.

Because we provide recommendations for monitoring your plant for the presence of L. monocytogenes, and for periodic sampling and testing of finished RF-RTE foods, we also provide recommendations for corrective actions to take if you detect L. monocytogenes in your plant or in food.

Because L. monocytogenes may be introduced into a food processing facility, we provide recommendations for training all employees as well as for training supervisors and other persons who are responsible for certain key operations.

We recommend that you make and keep certain records as an aid to controlling L. monocytogenes in your plant.

This document contains Appendices that describe procedures you can use to collect environmental samples and prepare those samples for analysis for L. monocytogenes. We refer you to the procedures that we use for detection and enumeration of L. monocytogenes in food and in the plant environment.

We recommend that any processor of a RF-RTE food, including processors of fresh-cut fruits and vegetables, and processors of frozen fruits and vegetables, follow the recommendations in this guidance. Our recommendations apply regardless of whether or not the food that is processed supports the growth of L. monocytogenes. The fact that a food does not support the growth of L. monocytogenes does not affect a manufacturer's responsibility under section 402(a)(4) of the Federal Food, Drug, and Cosmetic Act (the Act) to ensure that food is not prepared, packed, or held under insanitary conditions whereby it may become contaminated with filth, or whereby it may be rendered injurious to health.

We recommend that persons who transport RF-RTE foods follow the recommendations in section XV of this document.

In developing this guidance, we did not include specific recommendations that would apply to a person who harvests, picks, transports, or processes raw intact fruits and vegetables. Although persons who are engaged in these activities could find this guidance useful, we recommend that such persons refer to our guidance document entitled "Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables" as the primary guidance on preventing food-borne illness.

The "FDA Food Code" is a model code developed by FDA to assist and promote consistent implementation of national food safety regulatory policy among the local, State, and tribal governmental agencies that have primary responsibility for the regulation of oversight of retail level food operations. The FDA Food Code provides a scientifically sound technical and legal basis for regulating the retail and food service segment of the industry. The FDA Food Code also gives other users of the Food Code, such as educators, trainers and the retail and food service industries (restaurants and grocery stores and institutions such as nursing homes) up-to-date information on mitigating risk factors that can contribute to food-borne illnesses. Although the retail and food service industries may find the guidance in this document useful, we recommend that the retail and food service industries refer to the Food Code and its Annexes as the primary source of information on preventing food-borne illness. The FDA Food Code and its Annexes are available online.

In Title 21 of the Code of Federal Regulations (21 CFR part 110), we have established regulations for current good manufacturing practice (CGMP) in preparing, packing or holding food. These regulations include both binding requirements and non-binding recommendations relating to personnel, buildings and facilities, equipment, and production and process controls. In general, 21 CFR part 110 uses the word "shall" to identify binding requirements and the word "should" to identify non-binding recommendations. For example, under 21 CFR 110.80(a)(1), raw materials and other ingredients shall be inspected and segregated or otherwise handled as necessary to ascertain that they are clean and suitable for processing into food and shall be stored under conditions that will protect against contamination and minimize deterioration. Raw materials shall be washed or cleaned as necessary to remove soil or other contamination. Containers and carriers of raw materials should be inspected on receipt to ensure that their condition has not contributed to the contamination or deterioration of food.

The controls and practices provided in this guidance are recommendations and guidance to the refrigerated and frozen ready-to-eat foods industry. The recommendations in this guidance on control of L. monocytogenes in RF-RTE foods are recommendations that complement, but do not supersede, the requirements and recommendations in 21 CFR part 110. The recommendations in this guidance are intended to assist processors of RF-RTE foods in meeting the requirements and recommendations in 21 CFR part 110 with respect to the control of L. monocytogenes. They can also serve as a tool to be used by Federal and State regulatory officials in their evaluation of a firm's implementation of the requirements in 21 CFR part 110. This guidance provides information that would likely result in controls that are acceptable to FDA. However, it is not a binding set of requirements. Processors may choose to use other control measures to comply with the requirements in 21 CFR part 110, as long as they provide an equivalent level of assurance of safety for the product. However, processors who choose to use other control measures are responsible for establishing their adequacy.

For your convenience, in this document we identify those sections of 21 CFR part 110 that are most relevant to specific recommendations in this guidance. For example, under 21 CFR 110.40(g), compressed air or other gases mechanically introduced into food or used to clean food-contact surfaces or equipment shall be treated in such a way that food is not contaminated with unlawful indirect food additives. Within this guidance, we are making a specific recommendation for how to treat compressed gases used directly in or on RF-RTE foods, or on surfaces that contact RF-RTE foods. Because this specific recommendation is related to 21 CFR 110.40(g), we refer you to 21 CFR 110.40(g) when we state this recommendation. Importantly, it is your responsibility to comply with all applicable requirements in 21 CFR part 110, regardless of whether or not we refer to them in this guidance.

You can access 21 CFR part 110 on the Internet from the home page for FDA's Center for Food Safety and Applied Nutrition (CFSAN). For your convenience, when we refer you to a single section of 21 CFR part 110, we repeat the text of the section in this guidance. However, when we refer you to more than one section, we do not repeat the text of the section in this document, because it is simply impractical to do so.

The recommendations in this guidance do not change the applicability of other federal or state regulations or your responsibility to comply with those regulations. For example, if you process seafood for use as sushi, nothing in this guidance alters your responsibility to comply with the requirements of 21 CFR part 123 for Fish and Fishery Products. As another example, this guidance does not affect the responsibility of the Grade "A" dairy industry and the molluscan shellfish industries to operate in accordance with state regulations based on the Grade "A" Pasteurized Milk Ordinance and the National Shellfish Sanitation Program Model Ordinance, respectively.

In addition, in general the recommendations in this guidance complement, but do not supersede, recommendations that we have issued in other guidance documents. For example, if you process seafood for use as sushi, we continue to recommend that you follow the guidance in our document entitled "Fish and Fisheries Products. Hazards and Controls Guide".

We recommend that you refer to 21 CFR 110.3 for definitions of terms such as "adequate," "food-contact surface," "lot," "plant," and "rework."

In addition, in this section we define the following terms for the purpose of this guidance.

Clean in place (CIP) means a system used to clean process piping, bins, tanks, mixing equipment, or larger pieces of equipment without disassembly, where interior product zones are fully exposed and soil can be readily washed away by the flow of the cleaning solution.

Clean out of place (COP) means a system (e.g. cleaning tanks) used to clean equipment parts, piping, etc. after disassembly.

Critical food-contact surface means a surface that contacts food, or a surface from which drainage onto the food or onto surfaces that contact food ordinarily occurs during the normal course of operations after the food is subjected to a listericidal control process, or when the food is not subjected to any listericidal control process at the processor's facility.

Critical non-food-contact surface or area means a surface (other than a food-contact surface) or area that could, through the action of man or equipment, contaminate a food that will not be subjected to a listericidal control measure after the exposure of food or a food-contact surface to the surface or area. Critical non-food-contact surfaces and areas include equipment, vents, fixtures, drains, walls, floors, employee clothing, shoes, and accessories, and other surfaces in the plant that do not (or are not intended to) contact food.

Critical surfaces and areas mean critical food-contact surfaces and critical non-food-contact surfaces and areas.

Environmental sample means a sample that is collected from a surface or area of the plant for the purpose of testing the surface or area for the presence of Listeria species or L. monocytogenes.

Finished RF-RTE food means a refrigerated or frozen ready-to-eat food that is packaged.

High efficiency particulate air (HEPA) filter means an air filter that has an efficiency of 99.97 percent to 99.99 percent when tested using the dioctylphthalate (DOP) test with a particle size of 0.3 microns. Such filters can remove all yeast, mold, bacteria and other particles that are larger than 0.3 microns.

Listeria species means microorganisms within the genus Listeria, including L. monocytogenes.

Listericidal control measure means a control measure that will consistently destroy viable cells of L. monocytogenes and consistently lead to a finished food that contains less than 0.04 cfu of L. monocytogenes per gram (g) of food.

Listeristatic control measure means a control measure that has been scientifically demonstrated to prevent the growth of L. monocytogenes in a food.

Monitor means to conduct a planned sequence of observations or measurements to assess whether a process or procedure is under control.

Process or processing means any activity that is directly related to the production of a food, including any packaging activity.

Processor means any person engaged in commercial, custom, or institutional processing of a food.

Ready-to-eat (RTE) food means a food that is customarily consumed without cooking by the consumer, or that reasonably appears to be suitable for consumption without cooking by the consumer.

Screening test for Listeria species means a test that detects L. monocytogenes and other Listeria species.

We, us, and our refer to the U.S. Food and Drug Administration.

You, I, and my refer to the processor.

As discussed above (see Section II), the Risk Assessment estimated that some foods present a lower risk of transmission of foodborne illness than others. The foods that the Risk Assessment estimated to pose the lowest risk had physical or chemical characteristics that do not support the growth of L. monocytogenes. Therefore, we recommend that, whenever practical, you formulate a finished RF-RTE food using one or more of the following listeristatic control measures:

• pH less than or equal to 4.4;
• Water activity less than or equal to 0.92;
• Formulated to contain one or more inhibitory substances that, alone or in combination, prevent the growth of L. monocytogenes.

If you use a listeristatic control measure that is generally recognized to prevent the growth of L. monocytogenes (i.e., through control of pH or water activity), we recommend that you establish and implement controls to ensure that the control measure is consistently applied to your manufacturing process and is consistently achieved. For example, you could test each batch of material for pH or water activity in-process.

If you use a formulation that contains one or more inhibitory substances, we recommend that you demonstrate, through scientific studies, that the formulation consistently prevents the growth of L. monocytogenes. A listeristatic control measure is generally considered to be effective if growth studies show less than one log increase in the number of L. monocytogenes during replicate trials with the food of interest. For an example of how such studies are conducted, see Reference 20.

We also recommend that you establish and implement controls to ensure that any formulation designed to prevent the growth of L. monocytogenes is consistently applied to your manufacturing process and is consistently achieved. For example, you could establish a standard operating procedure in which one or more individuals (other than those responsible for batch operations) are responsible for verifying the addition of particular ingredients in specific amounts.

Freezing a food is generally recognized as effective in preventing the growth of any L. monocytogenes that may be present in the food. However, whether freezing can effectively prevent the transmission of foodborne illness when L. monocytogenes is present in low numbers depends on whether the frozen food is consumed in a frozen state (e.g., ice cream), or whether it is thawed and held in a refrigerator before consumption (e.g., frozen crabmeat). Thus, freezing could be an effective control for ice cream, but may not be an effective control for crabmeat.

Sections of 21 CFR part 110 that are applicable to the use of listeristatic control measures include 21 CFR 110.80(b)(4), which requires that measures such as sterilizing, irradiating, pasteurizing, freezing, refrigerating, controlling pH or controlling water activity, that are taken to destroy or prevent the growth of undesirable microorganisms, particularly those of public health significance, be adequate under the conditions of manufacture, handling, and distribution to prevent food from being adulterated within the meaning of the Act.

We recommend that you demonstrate, through scientific studies, that a listericidal control measure that you establish and use consistently destroys viable cells of L. monocytogenes and consistently leads to a finished food that contains less than 0.04 cfu/g of L. monocytogenes. Determining the extent of the process necessary to achieve that goal depends, in part, upon determining the likely levels of L. monocytogenes prior to application of the listericidal control measure. In the absence of scientific studies, a listericidal control measure that provides a reduction of the number of viable cells of L. monocytogenes of six orders of magnitude (six logarithms) may be acceptable to achieve that goal. This is called a "6D" process.

There are several approaches available for demonstrating that your process consistently destroys viable cells of L. monocytogenes, including:

• Reference to scientific literature or previous validation studies;
• Scientifically valid experimental trials; and
• Statistically designed surveys and/or mathematical modeling.

In looking for listericidal control measures, we recommend that you consider measures such as:

• Thermal processing;
• Irradiation, provided that irradiation has been approved and listed in 21 CFR part 179;
• Ultraviolet light, high pressure, or pulsed electric field; and
• Decontamination through the use of listericidal agents.

If you establish and use a listericidal control measure, we recommend that you establish and implement controls to ensure that the control measure is consistently applied to your manufacturing process and is consistently achieved.

When demonstrating that a listericidal control measure that you establish and implement is effective and when monitoring a listericidal control measure to ensure that it is consistently achieved, we recommend that you monitor parameters such as time, temperature, and concentration of a listericidal agent, on a continuous basis. If you determine that a listericidal control measure was not achieved or is otherwise ineffective, we recommend that you identify and implement appropriate corrective actions.

Sections of 21 CFR part 110 that are applicable to the use of listericidal control measures include 21 CFR 110.80(b)(4), which requires that measures such as sterilizing, irradiating, pasteurizing, freezing, refrigerating, controlling pH or controlling water activity, that are taken to destroy or prevent the growth of undesirable microorganisms, particularly those of public health significance, be adequate under the conditions of manufacture, handling, and distribution to prevent food from being adulterated within the meaning of the Act.

In this section, we recommend controls to reduce the potential that an ingredient or other raw material will contaminate a finished RF-RTE food with L. monocytogenes.

As discussed in the background section of this document (see section II), raw foods (such as raw seafood, raw produce, and unpasteurized milk) are potential sources of contamination with L. monocytogenes. In addition, because L. monocytogenes has been detected in a number of finished RF-RTE foods, a RF-RTE food that you purchase and use as an ingredient of a food that you manufacture is also a potential source of contamination.

We recommend that you establish a list of ingredients (such as raw foods) that are reasonably likely to be contaminated with L. monocytogenes and then establish controls that are appropriate for each of these ingredients. Depending on how an ingredient that you purchase is processed, it may be more or less likely to be contaminated with L. monocytogenes. For example, ingredients processed in the following manner are not reasonably likely to contain L. monocytogenes

• Aseptically processed and packaged;
• Retorted (e.g., canned);
• Ethylene oxide treated or irradiated in the package;
• Pasteurized (or equivalent treatment) in the package;
• Other approved lethal technologies (in the package)

We recommend that you handle raw foods, and any other food ingredients that could be contaminated with L. monocytogenes, as if they are contaminated with L. monocytogenes.

We recommend that you treat ingredients or other raw materials that are reasonably likely to be contaminated with L. monocytogenes with a listericidal control measure during the manufacturing process. For example, you could treat an ingredient before it is used in manufacture, or you could treat a mixture of ingredients at an in-process stage of manufacture.

If you do not use a listericidal control measure, then we recommend that you establish and implement controls designed to reduce the potential that the ingredient or other raw material received from a supplier is contaminated with L. monocytogenes. For example, you could:

• Obtain the ingredient under a supplier's Certificate of Conformance (COC) (guarantee). We recommend that any COC that you rely on in following this guidance include the period of guarantee and include a statement that the supplier's ingredients are produced under conditions that are consistent with this guidance.

• Obtain the ingredient under a supplier's Certificate of Analysis (COA). We recommend that any COA that you rely on in following this guidance include the sampling plan and the analytical results of testing to detect or enumerate Listeria species or L. monocytogenes, including the analytical method used and limits of the analytical method.
• Test the ingredient or other raw material for the presence of Listeria species or L. monocytogenes.

Although our recommended measures to control ingredients include obtaining an ingredient under a COA, or testing the ingredient yourself, testing a single lot of a food product for L. monocytogenes is of limited value in establishing the acceptability of that lot. It is preferable that your supplier produces food products under conditions that are consistent with this guidance. Product testing adds value primarily as part of a history of test results that is used to verify the adequacy of control measures over time.

If your supplier provides a COC, we recommend that you obtain that COC and conduct an on-site audit of the supplier on an annual basis. We also recommend that you periodically (e.g., weekly, monthly, or quarterly) test ingredients that you receive under a COC to verify the absence of L. monocytogenes.

If your supplier provides a COA, we recommend that you obtain the COA for each lot of ingredients, either prior to delivery or on receipt. We also recommend that you verify the results of the supplier's COA on each shipment of each lot of ingredients that you receive until you have enough experience with that supplier to be confident in the results provided on the COA. After that, we recommend that you continue to test ingredients that you receive under a COA on a periodic basis (e.g., weekly, monthly, or quarterly) to verify the absence of L. monocytogenes.

If you test an incoming ingredient for the presence of Listeria spp. rather than receive the ingredient under a COC or COA, we recommend that you:

• Test every lot of the ingredient if your final product supports the growth of L. monocytogenes; or
• Test incoming ingredients on a periodic basis (e.g., weekly, monthly, or quarterly) if your final product does not support the growth of L. monocytogenes.

For your convenience, in Table 3 we present these recommendations in the form of a decision tree.

Table 3. Decision Tree for Control of Ingredients

Sections of 21 CFR part 110 that are applicable to control of ingredients include 21 CFR 110.80, 110.80(a)(2) and 110.80(b)(4).

We recommend that you establish and implement procedures to minimize the amount of time that ingredients and other raw materials, in-process materials, and finished foods are stored. In particular, we recommend that you establish and follow procedures to use such materials on a first-in, first-out basis.

We also recommend that you transport and store ingredients and other raw materials, in-process materials, and finished foods at an internal temperature of less than or equal to 4 degrees C (less than or equal to 40 degrees F) and that you establish and use control measures to consistently achieve this internal temperature.

We also recommend that, during processing, you establish and use controls on the amount of time that ingredients and other raw materials, in-process materials, and finished foods are held above 4 degrees C (40 degrees F) and on the temperature during this time period.

Sections of 21 CFR part 110 that are applicable to storage practices to reduce the potential of foodborne illness from the consumption of a RF-RTE food include 21 CFR 110.40(e), 110.80(a)(5), 110.80(b)(2), 110.80(b)(3) and 110.80(b)(4).

We recommend that you provide training in employee health and hygienic practices for all employees and contractors who enter production and storage areas (e.g., employees who conduct production, maintenance, quality assurance, quality control, or warehousing operations), including employees and contractors who are temporary or seasonal. We also recommend that the training be conducted before the employee performs job activities with refresher training on an annual basis.

We recommend excluding employees who exhibit symptoms of gastroenteritis from working in food production areas.

We recommend that all persons who will enter an area where RF-RTE foods are processed or exposed thoroughly wash their hands before doing so. We also recommend that employees use suitable utensils (such as spatulas or tongs), or wear gloves, when touching exposed RF-RTE foods, food-contact surfaces, and packaging materials, and not touch exposed RF-RTE foods, food-contact surfaces, and packaging with bare hands.

We recommend that gloves and footwear worn by employees who handle RF-RTE foods or who work in areas where RF-RTE are processed or exposed be made of impermeable material, in good repair, easily cleanable or disposable, and used only in RF-RTE areas. Employees should not use cleated footwear unless it is necessary for their safety, because cleated footwear can collect large particles of dirt or other waste from the plant.

When gloves are used, we recommend that:

• Employees wash their hands before putting the gloves on;
• Multi-use gloves be washed and sanitized after the employee touches any non-food-contact surface;
• Single use gloves be discarded and replaced after the employee touches any non-food-contact surface; and
• Gloves worn outside areas where RF-RTE foods are processed or exposed (e.g., restrooms) be discarded before returning to the RF-RTE area.

We recommend that you consider the use of footbaths containing sanitizer when entering areas where RF-RTE foods are processed or exposed. We do not recommend the use of footbaths in dry processing environments, because the absence of water in the environment prevents the growth of L. monocytogenes. In dry environments it may be more appropriate to use a dry powdered sanitizer.

An example of a footbath is an automatic spray of foam disinfectant on the floor where people and equipment (such as carts and forklifts) enter the RF-RTE area. A footbath may also be a low flat container or a water tight recess in the floor with a non-slip surface and filled with a suitable sanitizer. If non-automatic footbaths are used, we recommend checking them at regular intervals, such as hourly, to ensure that they are filled with sanitizer and that the sanitizer is diluted to the proper concentration.

With respect to clothing, we recommend that:

• Employees not wear street clothes in areas where RF-RTE foods are processed or exposed unless the street clothes are adequately covered above the knees (e.g., with a clean smock);
• Smocks for employees in areas where RF-RTE foods are processed or exposed be worn only in the RF-RTE area and an adjacent vestibule (i.e., the area where the smock would be put on);
• Smocks be laundered or disposed of daily;
• Employees change into a clean uniform or smock before entering areas where RF-RTE foods are processed or exposed;
• Smocks or uniforms that will be used in areas where RF-RTE foods are processed or exposed be distinguished from smocks or uniforms that will be used in other areas (particularly areas where raw foods are processed or exposed) using a mechanism such as color coding; and
• Smocks or uniforms be distinguished according to the task that the employees perform (e.g., production or maintenance). For example, if you restrict the access of maintenance employees to areas of the plant where finished product is exposed, such color coding helps to identify the employees with such restricted access.

We recommend that you provide separate locker areas, break areas, and cafeteria areas for employees who handle RF-RTE foods and employees who handle raw foods. We also recommend that you ensure that employees who handle trash, offal, floor sweepings, drains, production waste, or scrap product do not handle RF-RTE food, and do not touch RF-RTE food-contact surfaces or food packaging material, unless they change their smocks or uniforms, wash and sanitize hands, wear clean gloves, and don and sanitize footwear.

We recommend that maintenance personnel in areas where RF-RTE foods are processed or exposed comply with the same hygiene requirements as production employees in those areas.

Sections of 21 CFR part 110 that are applicable to employee hygiene include 21 CFR 110.10(a), 110.10(b)(1), 110.10(b)(3), 110.10(b)(5), 110.10(b)(9), 110.10(c), and 110.37(f).

To reduce the potential for contamination of RF-RTE foods via air, aerosols, or traffic of employees or equipment, we recommend that you design and construct the plant to separate areas where RF-RTE foods are processed, exposed or stored from areas where raw foods are processed, exposed or stored, and from equipment washing areas, microbiological laboratories, maintenance areas, waste areas, offices, and toilet facilities. When possible, microbiological laboratories should be located as far away as possible from the processing area, preferably in another building. In designing the air flow in your plant, we recommend that you maintain positive air pressure on the RF-RTE side of the operation relative to the "raw" side (i.e., maintain higher air pressures in RF-RTE areas and lower air pressures in raw areas). We recommend that you consult individuals with appropriate engineering skills to determine how to achieve proper air balance, including determining the number, size, and location of intake and exhaust fans. Appendix 1 of this document provides some schematic diagrams relevant to these recommendations.

Figure 1 of Appendix 1 relates to air flow, and simply shows that the recommended air flow should have negative pressure in the raw processing area rather than in the RTE processing area. In Figures 2 and 3 of Appendix 1, we provide examples of plant design, including schematic recommendations related to air flow, product flow and the use of partitions in the design of the plant. In Figure 2 of Appendix 1, the example of a plant design has an additional partition between the raw processing area and the RTE processing area. In Figure 3, the example of a plant design does not have this additional partition between the raw processing area and the RTE processing area; instead, the plant design in Figure 3 relies on additional positive air pressure in the RTE processing area.

To reduce the potential for contamination of RF-RTE foods with microorganisms (including L. monocytogenes), we recommend that you design and construct the plant so that the air in rooms where RF-RTE foods are processed or exposed will be filtered. To remove bacteria (including L. monocytogenes) as well as yeasts and molds, we recommend that you filter the air in areas where RF-RTE foods are processed or exposed through High Efficiency Particle Air (HEPA) filters that have an efficiency of 99.97-99.99 percent at 0.3 micron. If you are not able to use such filters, we recommend that the final filter have an efficiency of at least 90-95 percent at 1 micron as rated in ASHRAE standard 52.2-1999.⁽⁵⁾ To avoid contamination of intake air, we recommend that the location of the air intake not be adjacent to the location of the air exhaust or other sources of airborne contamination such as waste disposal areas. Our recommendations to filter air are particularly important when major construction or remodeling occurs in an existing plant, because using air-tight barriers and limiting access between construction and food production areas can prevent introduction of contamination into the plant environment.

We recommend that water systems be adequately designed, installed, and maintained to prevent backflow and cross-connections between potable and non potable water lines or systems. We recommend that the areas for washing equipment that contacts RF-RTE foods be located in a room that is separate both from areas where RF-RTE foods are processed or exposed and from areas where equipment that contacts raw foods are washed.

To prevent the accumulation of standing water in or around drains, we recommend that:

• You design and construct the plant in a way that will make drains adequately accessible for cleaning and function;
• You eliminate trench drains in areas where RF-RTE foods are processed or exposed and replace them with enclosed plumbing to a floor drain; when this is not possible, we recommend that you equip trench drains for automatic flushing;
• You design and construct drains so that the drains conform to applicable plumbing codes and do not flow from areas where raw foods are processed or exposed to areas where RF-RTE foods are processed or exposed;
• You design and construct drains so that restroom drains are downstream of drains serving areas where RF-RTE foods are processed or exposed;
• The slope of floors to drains be at least 0.25 inch per foot (0.64 cm per 30.5 cm); and
• Sewer lines not be located above areas where RF-RTE foods, food-contact surfaces, or food packaging materials are processed or exposed. If this is not possible, we recommend that you take steps to protect RF-RTE foods from potential leakage, e.g., by shielding the sewer lines to prevent or convey leakage.

We recommend that you design and construct the plant in a manner that will prevent condensate from contacting exposed RF-RTE foods, food-contact surfaces, and food packaging material. Measures that can help prevent the formation of condensate include exhausting vapors from cooking operations, using dehumidifiers, and providing adequate ventilation.

We recommend that you design and construct the plant so that walls, ceilings, windows, doors, floors, drains, and overhead fixtures (e.g. pipes, air vents, and lights) in areas where RF-RTE foods are processed or exposed are accessible for cleaning, resist deterioration by product or cleaning chemicals, and prevent harborage of microorganisms. We also recommend that you design and construct the roof so that it drains freely and does not leak. We recommend that you not place windows that can be opened in areas where RF-RTE foods are processed or exposed. To prevent harborage of microorganisms, we also recommend not using construction materials made of wood in areas where RF-RTE areas are processed or exposed and in other wet processing areas in the facility.

Sections of 21 CFR part 110 that are applicable to the design and construction of the plant include 21 CFR 110.20(b)(2), 110.20(b)(4), 110.20(b)(6), 110.20(b)(7), 110.20(d)(4), 110.35(a), 110.35(c), 110.37(b), 110.40(a), and 110.80(b)(13).

To minimize the potential for transfer of L. monocytogenes between areas where raw foods are processed or exposed and areas where RF-RTE foods are processed or exposed, we recommend that you control traffic flow patterns for employees, food products, and equipment.

In areas where RF-RTE foods are processed or exposed, we recommend that you use pallets that can easily be cleaned and keep them in good condition, and that you not use wood pallets in areas where RF-RTE foods are processed or exposed or in other areas for wet processing and storage. We also recommend that you clean and sanitize pallets and wheels of transport equipment (e.g., carts, forklifts, and mobile racks) before they enter an area where RF-RTE foods are processed or exposed. We recommend that you designate one set of equipment such as carts, forklifts, mobile racks, and pallets to areas where raw foods are processed or exposed and designate a separate set of such equipment to areas where RF-RTE foods are processed or exposed.

With respect to containers, we recommend that you:

• Distinguish between containers used for product, rework, or waste;
• Clearly label containers;
• Select containers that can easily be cleaned;
• Dedicate containers by function (e.g., in-process products, rework and waste);
• Dedicate containers by area (e.g., use one set of containers in areas where RF-RTE foods are processed or exposed and a different set of containers in areas where raw foods are processed or exposed); and
• Use a mechanism such as color-coding to identify containers by function and area.

We recommend that you use a mechanism such as color-coding to distinguish between portable equipment (such as utensils, racks, and totes) that is used with RF-RTE foods and portable equipment that is used with raw foods.

We recommend that you discard or decontaminate continuous use brines and recycled process water used in direct contact with RF-RTE with sufficient frequency to control L. monocytogenes (see our recommendations in Appendix 2). To decontaminate such brines and water, we recommend that you use measures such as chlorination, heat treatment, or other effective treatment. In determining the frequency of decontamination treatment, you should consider the results of environmental monitoring for L. monocytogenes (see section XVI of this document).

To prevent aerosols from contacting RF-RTE food, food-contact surfaces and food packaging materials, employees should not use high-pressure water hoses in areas where RF-RTE foods are processed or exposed during production or after equipment has been cleaned and sanitized.

Sections of 21 CFR part 110 that are applicable to the operation of the plant include 21 CFR 110.35(a), 110.40(a), 110.80(a)(2), 110.80(a)(5), 110.80(b)(1), and 110.80(b)(6).

We recommend that you dry and filter compressed gases or air used directly in or on RF-RTE food, or on RTE food-contact surfaces. We recommend that dehydration be done at the source of gas or air supply and that filtration be done at the point of use, using a filter that can retain particles larger than 0.3 micron. You should take appropriate steps to maintain the filters.

We recommend that you maintain and inspect water treatment systems to ensure that they do not become a source of microbial contamination. We also recommend that you handle and store ice and ice utensils in a manner that protects ice from microbial contamination.

We recommend that you make mixed hot and cold water available at hand washing stations.

Sections of 21 CFR part 110 that are applicable to the use of compressed gas, water and ice include 21 CFR 110.37(a), 110.37(e), 110.40(g), 110.80(a)(1), and 110.80(b)(16).

We recommend that the equipment that you purchase and use to process RF-RTE foods be designed and constructed to facilitate cleaning and to minimize sites where microbial harborage and multiplication can occur. We also recommend that you or the manufacturer of the equipment review the design of equipment regardless of whether the equipment is new or existing, including existing equipment that is being modified.

We recommend that you design and construct equipment such as catwalk framework, table legs, conveyor rollers, and racks so that they cannot collect water that could harbor L. monocytogenes (e.g. not hollow or foam filled). Ladders and stairs in areas where RF-RTE foods are processed or exposed should have plating underneath that prevents any debris from shoes or other items from personnel who are using them from falling onto the processing line. We recommend that these plates have up-turned edges so that debris that falls onto the plates cannot roll off and onto the lines.

To prevent contamination of RF-RTE foods, we recommend that you not position catwalks and stairs with open grating over exposed RF-RTE food or food-contact surfaces. To prevent contamination of stationary equipment used to process RF-RTE foods, you should not install such equipment over floor drains. We recommend that to prevent contamination of RF-RTE foods and food-contact surfaces from floor splash, you should sufficiently elevate food-contact surfaces (including conveyors) above the floor. When possible, you should avoid overhead conveyors. If overhead conveyors cannot be avoided, we recommend that they be designed to be easily accessible for cleaning. To prevent contamination of RF-RTE food and food-contact surfaces from wheel spray, we recommend that you place cleanable cover guards over the wheels of racks used for transporting exposed RF-RTE foods.

We recommend that you add listericidal substances (e.g., sodium benzoate) to lubricants (e.g., chain, valve, and seal lubricants) so that the lubricants do not become contaminated with product residue and, thus, become a niche for L. monocytogenes.

We recommend that condensate from refrigeration evaporation coils be directed to a drain through a hose or, alternatively, collected in a pan that drains through a hose or suitable pipe to a drain. An air gap or other back flow mechanism should be in the drain line to prevent back flow from the sewer system to the drip pan. We recommend that you regularly inspect the pan and drain to ensure that the hose or pipe does not become clogged.

To prevent hose nozzles and employee hands from becoming contaminated, we recommend that you keep hose nozzles off the floor or other unclean surfaces unless they are not intended to make contact with RF-RTE food, food-contact surfaces, or packaging material. For example, you could install and use automatically retractable hoses (including spring tension or spring loaded retractable hoses) or fixed length hoses that do not touch the floor.

If you use raw product to cool RF-RTE product, we recommend that heat exchangers have higher pressure on the RF-RTE side than on the raw side.

We recommend that food-contact surfaces be smooth, non-absorbent, sealed, easily cleanable, sloped to drain freely, and made of durable, non-corrosive and non-toxic materials. We also recommend that food-contact surfaces be smoothly bonded (e.g., free of pits, folds, cracks, crevices, open seams, cotter pins, exposed threads and piano hinges) and that junctures be covered. Piping used to convey RF-RTE foods should not have dead ends or cross-connections between raw and RF-RTE foods.

Sections of 21 CFR part 110 that are applicable to the design and construction of equipment include 21 CFR 110.20(b)(4), 110.37(b)(3), 110.40(a), 110.40(b), 110.40(c), and 110.40(d).

We recommend that you establish and use a preventive maintenance program that is designed to minimize breakdowns and prevent contamination that could occur during repair of equipment. We recommend that such a preventive maintenance program include a written program containing defined schedules for examination and maintenance of equipment such as valves, gaskets, o-rings, pumps, screens, filters, and heat exchanger plates.

We recommend that you examine and change filters used on intake air either at a frequency based on the manufacturer's specification or more frequently based on pressure differential or the results of environmental monitoring.

We recommend that tools intended for maintenance of equipment used in areas where RF-RTE foods are processed or exposed be dedicated to those areas and be washed and sanitized prior to use.

We recommend that equipment and food-contact surfaces used in areas where RF-RTE foods are processed or exposed be cleaned and sanitized after maintenance and prior to use in production. Equipment that could become contaminated as a result of maintenance on facility utilities (e.g., air or water systems) or remodeling should be cleaned and sanitized prior to use.

Sections of 21 CFR part 110 that are applicable to maintenance of equipment include 21 CFR 110.35(d)(1), 110.40(a), 110.40(g), 110.80(b)(1), and 110.80(b)(2).

To minimize the potential for contamination of RF-RTE food and food-contact surfaces with L. monocytogenes, we recommend that you establish and use a sanitation program that includes a written sanitation standard operating procedure (SSOP) and a sanitation maintenance schedule for areas where RF-RTE foods or food-contact surfaces are processed or exposed. In general, we recommend that a written SSOP address:

• The condition and cleanliness of food-contact surfaces, including equipment, utensils, gloves, and outer garments; and
• The prevention of cross-contamination:
  • From insanitary objects to food;
  • From insanitary objects to food packaging material and other food-contact surfaces (including equipment, utensils, gloves, and outer garments);
  • From raw food to cooked food;
  • After any listericidal step; and
  • As a result of traffic flow patterns for employees and for equipment.

We recommend that if you establish a written SSOP that you make the SSOP readily available to personnel who are responsible for cleaning and that you monitor adherence to the SSOP. We provide recommendations for schedules for routine cleaning and sanitation in Appendix 2.

We recommend that SSOPs for cleaning equipment and floors identify:

• Equipment or area to be cleaned;
• Disassembly of equipment, if applicable;
• Frequency of cleaning;
• Type and concentration of cleaning compounds and sanitizers;
• Time/temperature of cleaning solutions; and
• Flow rate (velocity) or pressure of cleaning solution, if applicable.

We recommend that SSOPs for cleaning and sanitizing equipment include the following steps:

• Removal of heavy soil or debris from equipment, if needed;
• Pre-rinsing the equipment;
• Foaming and scrubbing the equipment with an effective cleaner;
• Rinsing the equipment after treating it with the cleaner;
• Sanitizing equipment; and
• Visual inspection of food-contact surfaces for residues of cleaning agents or sanitizing agents.

We recommend that SSOPs for cleaning and sanitizing floors include the following steps:

• Removal of heavy soil or debris from floors (e.g., with brooms or shovels), if needed;
• Cleaning other debris from floors;
• Rinsing floors with water using a low pressure/low volume hose;
• Using a dedicated brush or floor scrubber to scrub floors with an effective cleaner, applying water as needed;
• Thoroughly rinsing floors using a low pressure/low volume hose;
• Sanitizing floors; and
• Removing excess water from floors if needed.

For clean-in-place (CIP) systems, we recommend that you monitor the concentration of cleaning solutions and sanitizers and verify flow rate, duration of the cleaning cycle and temperature. For clean-out-of-place (COP) systems, we recommend that you monitor the concentration of cleaning solutions and sanitizers.

With respect to wet cleaning, we recommend that you:

• Not perform wet cleaning of equipment (e.g., down lines, storage and spiral coolers, and spiral freezers) in a room where RF-RTE food is exposed, even if you cover the RF-RTE food (e.g., with plastic or paper);
• If wet cleaning does occur, remove all exposed RF-RTE food from a room before beginning any wet cleaning of equipment, floors, etc; and
• Remove all exposed RF-RTE food from a cooler prior to cleaning the cooler, refrigeration condenser units or condensate drip pans and hoses.

When assembling cleaned and sanitized equipment (e.g., pump impellers, pipes), you should not place the equipment directly on the floor. We recommend that you take steps to prevent water from the floor or unclean equipment from splashing onto clean equipment.

When using CIP systems, we recommend that you dedicate separate CIP systems for cleaning equipment used to process RF-RTE food and for cleaning equipment used to process raw food. If you are unable to designate separate CIP systems and, thus, use a common CIP system, we recommend that you maintain the temperature of an alkaline cleaning solution at or above 71 degrees C (160 degrees F).

When using COP systems (e.g., wash tanks), we recommend that you dedicate separate COP systems for cleaning equipment used to process RF-RTE food and for cleaning equipment used to process raw food.

We recommend that all wipes be disposable and discarded after each use on RTE food-contact surfaces and that scouring pads be discarded daily. When scouring pads are not in use during the day, we recommend they be kept dry or placed in a sanitizer solution.

We recommend that you maintain and clean equipment used for cleaning (e.g., brushes, mops, floor scrubbers, and vacuum cleaners) so that it does not become a source of contamination. We recommend that you dedicate cleaning equipment either to areas where RF-RTE foods are processed or exposed, or to areas where raw foods are processed or exposed, using a mechanism (such as color coding) that easily distinguishes the equipment dedicated to the two areas.

Sections of 21 CFR part 110 that are applicable to a general sanitation program include 21 CFR 110.35(a), 110.35(d)(1), 110.80(b)(1), and 110.80(b)(7).

We recommend that you clean and sanitize floor drains in a manner that prevents contamination of other surfaces in the room. To do so, we recommend that:

• You not clean floor drains during times when RF-RTE foods are processed or exposed;
• You not use high-pressure hoses to clear or clean a drain, because use of such hoses could create aerosols that may spread contamination throughout the room;
• Brushes used to clean floor drains be at least ¼ inch (0.64 cm) smaller than the diameter of the drain opening;
• You use a splashguard to prevent splashing during cleaning;
• Utensils that you use for cleaning drains be dedicated to that purpose and be easily distinguishable from utensils used for other purposes (e.g., by color-coding).

If a drain backs up and water flows into an area where RF-RTE foods are being processed or exposed, we recommend that you take steps to avoid splashing any equipment and follow the sequence of steps described below to clear the drain and clean the area around it:

• Stop any production;
• Remove any uncovered RF-RTE foods from the affected area;
• Clear the drain;
• Clean the affected area with an effective cleaner, rinse it, and sanitize it; and
• Remove excess water from the floor.

After cleaning a drain, we recommend that employees change clothes and wash and sanitize hands before touching a RF-RTE food-contact surface.

If you use bactericidal drain rings, we recommend that you monitor them and replace them when appropriate.

Sections of 21 CFR part 110 that are applicable to cleaning drains include 21 CFR 110.10(b)(1), 110.10(b)(3), 110.35(a), and 110.37(b)(3).

Sanitizers containing quaternary ammonium compounds (QACs), peroxyacetic acid, iodine, or chlorine have been used to control L. monocytogenes in various situations (Ref. 5). We recommend the use of QACs for many applications, because QACs have been found to be effective against L. monocytogenes and leave a residual germicidal effect on surfaces (Ref. 5). We note that peroxyacetic acid sanitizers have been shown to be effective against biofilms containing L. monocytogenes (Ref. 5). We recommend that you rotate sanitizers, because this has been reported to provide for greater effectiveness (Ref. 5).

Sanitizers are subject to registration under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), which is administered by the U.S. Environmental Protection Agency. You should use sanitizing solutions in accordance with the conditions of use authorized under FIFRA, which should be on the product label. You should direct questions regarding the use of the sanitizer to control L. monocytogenes to the supplier of the sanitizer, who may have specific recommendations regarding factors (such as temperature, pH, and water hardness) that could influence the effectiveness of the sanitizer.

Hot water or steam has been used to sanitize racks and equipment that is difficult to clean (Ref. 5).

Sections of 21 CFR part 110 that are applicable to sanitizing procedures and solutions include 21 CFR 110.35(a), 110.35(b), 110.35(d), 110.35(d)(1), 110.35(d)(2), 110.35(d)(5), and 110.80(b)(1).

We recommend that you monitor sanitation conditions and practices during processing with sufficient frequency to ensure the cleanliness of food-contact surfaces and prevent cross-contamination. We also recommend that you correct, in a timely manner, any monitored sanitation conditions, cleanliness and practices that are not implemented in accordance with your SSOP.

Sections of 21 CFR part 110 that are applicable to sanitation monitoring include 21 CFR 110.35(a), which requires, in relevant part, that cleaning and sanitizing of utensils and equipment be conducted in a manner that protects against contamination of food, food-contact surfaces, or food-packaging materials.

We recommend that you establish and maintain sanitation control records that document:

• Your sanitation monitoring; and
• Corrections of monitored sanitation conditions and practices that are not implemented in accordance with your SSOP.

We recommend that you inspect transportation vehicles for structural integrity, cleanliness, and overall suitability when unloading ingredients and prior to loading finished products. We also recommend that you use transportation vehicles that are adequately equipped to control and monitor the temperature of incoming ingredients and outgoing finished food products on a continuous basis.

We recommend that any tankers used to transport ingredients or finished food products be dedicated to those specific uses and that you verify that the tanker has been adequately cleaned and sanitized prior to use.

Sections of 21 CFR part 110 that are applicable to transportation include 21 CFR 110.93, which requires that storage and transportation of finished food be under conditions that will protect food against physical, chemical, and microbial contamination as well as against deterioration of the food and the container.

See Section VI for the definitions that we are using in this document for the terms:

• Critical food-contact surface;
• Critical non-food-contact surface or area; and
• Critical surfaces and areas.

We recommend that you establish and implement a written plan for the collection of environmental samples from critical surfaces and areas, and for testing those samples for the presence of Listeria species or L. monocytogenes. We recommend that you evaluate each plant, product, and process to determine the appropriate monitoring points.

We recommend that your program use screening tests for the presence of Listeria species because these tests usually are more rapid than tests for L. monocytogenes. We recommend that you either test the individual samples that you collect, or test a composite that you make from multiple samples taken from a given area. We describe recommended procedures for compositing samples in Appendix 4.

For critical food-contact surfaces, we recommend that your written plan include collection and testing environmental samples from all, or representative sets of, such surfaces at least once every week. If you will test a representative set of samples (rather than all samples) each week, we recommend that your plan for sample collection and testing be designed so that all critical food-contact surfaces are tested at least once each month. The most important time to collect these environmental samples is at a time that is both prior to cleanup and no sooner than the middle of production.

The number of samples that you should collect depends on the size of your production lines (Refs. 5, 6, 9 and 10). We recommend that even the smallest processors collect samples from a minimum of 5 sites of food-contact surfaces in each production line for RF-RTE foods. We recommend that larger processors determine the appropriate number of sampling sites based on the size of the facility. If you consistently see negative test results, we recommend that you add other surfaces to your plan for sample collection and testing. For examples of food-contact surfaces to sample, see the sites that we identify as potential sources of contamination with L. monocytogenes in section C of Table 1 (see section II, above).

For critical non-food-contact surfaces and areas, we recommend that your written plan include collection and testing of environmental samples from all, or representative sets of, such surfaces and areas at least once every two weeks. If you will test a representative set of samples (rather than all samples) each time, we recommend that your plan for sample collection and testing be designed so that all critical non-food-contact surfaces are tested at least once each quarter. Such samples could be taken at any time (e.g., pre-production but post-sanitation; during production; or after production).

The number of samples that you should collect depends on the size of your production lines (Refs. 5, 6, 9, and 10). We recommend that even the smallest processors collect samples from a minimum of 5 sites in each area where RF-RTE foods are processed, exposed, or stored. We recommend that larger processors determine the appropriate number of sampling sites based on the size of the facility. In identifying the sites within each area, we recommend that you focus on areas of high traffic and/or high moisture. We recommend that you vary the sites of sample collection on a rotating basis, particularly if you consistently see negative test results. For examples of sites to sample, see the sites that we identify as potential sources of contamination with L. monocytogenes in sections D and E of Table 1 (see section II, above).

We describe recommended procedures to collect environmental samples in Appendix 3.

Sections of 21 CFR part 110 that are applicable to monitoring critical surfaces and areas include 21 CFR 110.80, which requires, in relevant part, that chemical, microbial, or extraneous-material testing procedures be used where necessary to identify sanitation failures or possible food contamination.

We recommend that you establish and implement a written plan for the periodic collection of samples of finished RF-RTE food, and for testing those samples for the presence of Listeria species or L. monocytogenes. The purpose of the recommended periodic sample collection and testing is to provide a historical reference for your production facility and to validate the adequacy of your controls rather than to determine whether to release individual lots of RF-RTE food that you process. We recommend that your written plan include the frequency of sampling and the sampling plan to accomplish those goals. For recommendations on corrective actions to take if you find Listeria species or L. monocytogenes in samples of finished RF-RTE food, see Sections XIX and XX.

Sections of 21 CFR part 110 that are applicable to sampling of finished foods include 21 CFR 110.80, which requires, in relevant part, that chemical, microbial, or extraneous-material testing procedures be used where necessary to identify sanitation failures or possible food contamination.

If you detect contamination of a critical food-contact surface or food with Listeria species, we recommend that you either conduct a test to determine whether the Listeria species is L. monocytogenes, or assume that the Listeria species is L. monocytogenes. Sections of 21 CFR part 110 that are applicable to this recommendation include 21 CFR 110.80, which requires, in relevant part, that chemical, microbial, or extraneous-material testing procedures be used where necessary to identify sanitation failures or possible food contamination.

If you determine that the Listeria species is NOT L. monocytogenes, we recommend that you take corrective actions regarding your plant and your processing, because the presence of any Listeria species suggests that conditions also are suitable for survival and/or growth of L. monocytogenes. In section XIX of this document, we describe our recommended corrective actions for your plant and your processing and provide citations to applicable sections of 21 CFR part 110.

If you either determine or assume that the Listeria species IS L. monocytogenes, we recommend that you take the corrective actions that we describe in sections XIX and XX of this document. In Section XIX, we describe our recommendations regarding your plant and your processing and provide the citations to applicable sections of 21 CFR part 110. In Section XX, we describe our recommendations regarding food and provide citations to applicable sections of 21 CFR part 110.

If you detect Listeria species or L. monocytogenes on a critical surface or area or in food, we recommend that you follow a corrective action plan that describes the steps to be taken, and assigns responsibility for taking those steps, to ensure that the cause of the contamination is corrected. We recommend that a corrective action plan include the following corrective actions:

• Conduct additional sampling and testing as appropriate to determine the specific surface or area that is contaminated with Listeria species or L. monocytogenes. For example, if you initially tested a composite sample, we recommend that you determine the source of the contamination, either by testing the individual samples that had been combined to form the composite or by collecting additional individual samples from the affected area and testing the new samples; and
• Clean and sanitize the contaminated surface or area; and
• Conduct additional sampling and testing to determine whether the contamination has been eliminated. If test results from the additional testing continue to be positive for Listeria species or L. monocytogenes, we recommend that you continue to clean, sanitize, sample and test until the test results demonstrate that the contamination with Listeria species or L. monocytogenes has been eliminated; and
• Review production, maintenance and sanitation procedures to determine whether to modify the procedures to prevent contamination and make those modifications; and
• Review the scenarios that we provide in Table 2 (see Section II of this document) as an aid to identifying causes of contamination; and
• Check maintenance records for modifications or repairs to major equipment; and
• Interview and observe sanitation, maintenance, and production employees to determine whether procedures were followed; and
• Correct any identified problems that could lead to contamination.

We also recommend that you make and keep a record of all corrective actions taken.

Sections of 21 CFR part 110 that are applicable to corrective actions in your plant if you detect Listeria species or L. monocytogenes on a critical surface or area or in food include 21 CFR 110.35(d), which requires that all food-contact surfaces, including utensils and food-contact surfaces of equipment, be cleaned as frequently as necessary to protect against contamination of food.

Sections of 21 CFR part 110 that are applicable to corrective actions in your processing if you detect Listeria species or L. monocytogenes on a critical surface or area or in food include 21 CFR 110.80 and 110.80(b)(2).

In this section, we provide two sets of recommendations for corrective actions that you should take regarding food if you detect L. monocytogenes on a critical food-contact surface or in food (or if you assume that Listeria species on a critical food-contact surface or in food is L. monocytogenes). Our recommendations depend on whether the food does, or does not, support the growth of L. monocytogenes.

We recommend that you establish and follow a corrective action plan that describes the steps to be taken, and assigns responsibility for taking those steps, to ensure that no finished RF-RTE food that supports the growth of L. monocytogenes enters commerce if:

• The food bears or contains greater than or equal to 0.04 cfu of L. monocytogenes per gram of food; or
• The food has been prepared, packed, or held under insanitary conditions whereby it may have become contaminated with filth, or whereby it may have been rendered injurious to health.

We recommend that such a corrective action plan include the following steps:

• Segregate and hold any food that may have contacted the contaminated food-contact surface until you have determined and taken appropriate corrective actions. For example, segregate and hold any food that was in contact with the contaminated food-contact surface since the last time that a test was negative for Listeria species or L. monocytogenes on that food-contact surface or since the last time that food-contact surface was cleaned and sanitized;
• Determine and take appropriate corrective action for any food that may have contacted the contaminated food-contact surface. Examples of recommended corrective actions include:
  • Treating the food with a listericidal control measure;
  • Reprocessing the food so that the food:
    • Does not support the growth of L. monocytogenes; and
    • Contains less than 100 cfu of L. monocytogenes per gram of food;
  • Diverting the food to use by animals (as long as such diversion would not adulterate the food for animals);
  • Diverting the food to a use in which it will not be consumed;
  • Destroying the food;
  • Recalling finished RF-RTE food that has been distributed.

We recommend that you establish and follow a corrective action plan that describes the steps to be taken, and assigns responsibility for taking those steps, to ensure that no finished RF-RTE food that does not support the growth of L. monocytogenes enters commerce if:

• The food bears or contains greater than or equal to 100 cfu of L. monocytogenes per gram of food; or
• The food has been prepared, packed, or held under insanitary conditions whereby it may have become contaminated with filth, or whereby it may have been rendered injurious to health.

We recommend that such a corrective action plan include the following corrective actions:

• Segregate and hold any food that may have contacted the contaminated food-contact surface until you have determined and taken appropriate corrective actions. For example, segregate and hold any food that was in contact with the contaminated food-contact surface since the last time that a test was negative for Listeria species or L. monocytogenes on that food-contact surface or since the last time the surface was cleaned and sanitized;
• Determine and take appropriate corrective action for any food that may have contacted the contaminated food-contact surface. Examples of recommended corrective actions include:
  • Treating the food with a listericidal control measure;
  • Testing samples of the food to determine the number of L. monocytogenes, and not distributing any food that has greater than or equal to 100 cfu of L. monocytogenes per gram of food;
  • Diverting the food to use by animals (as long as such diversion would not adulterate the food for animals);
  • Diverting the food to a use in which it will not be consumed;
  • Destroying the food;
  • Recalling finished RF-RTE food that has been distributed.

We recommend that you make and keep a record of all corrective actions taken.

Sections of 21 CFR part 110 that are applicable to corrective actions regarding food if you detect L. monocytogenes on a critical food-contact surface (or if you assume that Listeria species that you detect on a critical food contact surface is L. monocytogenes) include 21 CFR 110.80, which requires that all reasonable precautions be taken to ensure that production procedures do not contribute contamination from any source and that chemical, microbial, or extraneous-material testing procedures be used where necessary to identify sanitation failures or possible food contamination.

Sections of 21 CFR part 110 that are applicable to corrective actions regarding food if you detect L. monocytogenes in food (or if you assume that Listeria species that you detect in food is L. monocytogenes) include 21 CFR 110.80 and 110.80(b)(9).

We recommend that you provide training in employee health and hygienic practices for all employees and contractors who enter production and storage areas (e.g., employees who conduct production, maintenance, quality assurance, quality control, or warehousing operations), including employees and contractors who are temporary or seasonal. We also recommend that the training be conducted before the employee performs job activities, with refresher training on an annual basis.

We recommend that personnel who supervise or are otherwise responsible for the operations listed below successfully complete training in the application of the principles of the practices recommended in this guidance to the control of L. monocytogenes in RF-RTE food.

• Establishing effective listericidal and listeristatic control measures and ensuring that such control measures consistently operate as intended;
• Collecting and testing environmental samples and samples of finished RF-RTE foods;
• Determining and taking corrective actions; and
• Establishing and using sanitation standard operating procedures and conducting associated monitoring.

Sections of 21 CFR part 110 that are applicable to training include the recommendations in 21 CFR 110.10(c) and the requirements in 21 CFR 110.10(d).

We recommend that you use the procedures described in Appendix 4 for preparing environmental samples for analysis. We recommend that you use the procedures described in FDA's Bacteriological Analytical Manual Online (BAM), Chapter 10 - "Listeria monocytogenes," "Detection and Enumeration of Listeria monocytogenes in Foods" (Ref. 22) for preparing food samples for analysis.

We recommend that you use the analytical methods in FDA's BAM (Ref. 22) to:

1. Detect the presence of Listeria species or L. monocytogenes in environmental samples;
2. Detect the presence of Listeria species or L. monocytogenes in RF-RTE Foods that support the growth of L. monocytogenes; and
3. Confirm whether Listeria species is L. monocytogenes.

We recommend that you use ISO 11290-2:1998(E) "Microbiology of food and animal feeding stuffs - Horizontal method for the detection and enumeration of Listeria monocytogenes - Part 2: Enumeration method" to enumerate L. monocytogenes in RF-RTE foods that do not support its growth. (ISO 11290-2:1998/Amd. 1:2004(E) "Microbiology of food and animal feeding stuffs - Horizontal method for the detection and enumeration of Listeria monocytogenes - Part 2: Enumeration method AMENDMENT 1: Modification of the enumeration medium" amends ISO 11290-2:1998(E). The amendment uses ALOA agar instead of PALCAM agar. If ALOA agar is not commercially available in the United States, we recommend that you use PALCAM according to ISO 11290-2:1998(E)). ISO methods are available from the International Organization for Standardization

If you use analytical methods other than those provided in the BAM or by ISO, we recommend that you use written methods that have equivalent or greater sensitivity for detecting and enumerating Listeria species and L. monocytogenes and for confirming the presence of L. monocytogenes.

We recommend that you make and keep the following records:

• Documentation of listeristatic control measures;
• Documentation of listericidal control measures;
• Your list of ingredients and other raw materials that are reasonably likely to be contaminated with L. monocytogenes;
• Any Certificate of Analysis or Certificate of Conformance (i.e., supplier's guarantee) that you rely on to control L. monocytogenes in ingredients;
• A written plan that you establish and implement for collecting and testing environmental samples;
• A written plan that you establish and implement for sampling and testing a finished RF-RTE food;
• Any written analytical method (other than the methods provided in FDA's BAM or by ISO) that you use to detect or enumerate Listeria species or L. monocytogenes, including the sensitivity of the method;
• The results of any tests that you conduct to detect or enumerate Listeria species or L. monocytogenes;
• Documentation of any corrective actions taken;
• A written sanitation standard operating procedure; and
• Sanitation control records.

We recommend that these records include:

• Your name and address;
• The date and time of the activity that the record reflects;
• Actual values observed, when applicable;
• The signature or initials of the person performing the operation, and the date of the signature or initials; and
• Where appropriate, the identity of the finished food and the production code, if any.

We recommend that you enter processing and other information on records at the time that it is observed.

We recommend that you retain records for 2 years and review and update, as needed, your written plans at least once a year.

We have placed the following references on display in the Division of Dockets Management, Food and Drug Administration, 5630 Fishers Lane, rm. 1061, Rockville, MD 20852. Unless otherwise specified, we placed the references in Docket No. 2007D-0494. You may see them at that location between 9 a.m. and 4 p.m., Monday through Friday.

1. U.S. Food and Drug Administration, and U.S. Food Safety and Inspection Service. 2003. Quantitative Assessment of the Relative Risk to Public Health from Foodborne Listeria monocytogenes Among Selected Categories of Ready-to-Eat Foods. Available in Docket No. 1999N-1168, Vols. 23 through 28, and at Quantitative Assessment of Relative Risk to Public Health from Foodborne Listeria monocytogenes Among Selected Categories of Ready-to-Eat Foods
2. National Advisory Committee on Microbiological Criteria for Foods. 1991. Listeria monocytogenes. Recommendations by The National Advisory Committee on Microbiological Criteria for Foods. International Journal of Food Microbiology 14 (3-4): 185-246. Available in Docket No. 1999N-1168, Volume 0015 bkg1 (12 of 17), Tab 287.
3. Fenlon DR, Wilson J, and Donachie W. 1996. The incidence and level of Listeria monocytogenes contamination of food sources at primary production and initial processing. Journal of Applied Bacteriology 81 (6): 641-650. Available in Docket No. 1999N-1168, Volume 0011 bkg1 (08 of 17), Tab 134.
4. Fenlon DR. 1999. Listeria monocytogenes in the natural environment. eds ET Ryser and EH Marth, 21-37. New York: Marcel Dekker, Inc. Available in Docket No. 1999N-1168, Volume 0009 bkg1 (06 of 17), File name bkg0001_5_a.pdf.
5. Tompkin RB, Scott VN, Bernard DT, Sveum WH, and Gombas KS. 1999. Guidelines to Prevent Post-Processing Contamination from Listeria monocytogenes. Dairy, Food and Environmental Sanitation 19 (8): 551-562.
6. Tompkin RB. 2002. Control of Listeria monocytogenes in the food-processing environment. Journal of Food Protection 65 (4): 709-725.
7. Moretro T, and Lansgrund S. 2004. Listeria monocytogenes: Biofilm Formation and Persistence in Food Processing Environments. Biofilms 1: 107-121.
8. Gall K, Scott VN, Collette R, Jahncke M, Hicks D, and Wiedmann M. 2004. Implementing Targeted Good Manufacturing Practices and Sanitation Procedures to Minimize Listeria Contamination of Smoked Seafood Products. Food Protection Trends 24 (5): 302-315.
9. Kornacki JL. 2005. Controlling Listeria in the Food Processing Environment. Food Technology 59 (11): 36-42.
10. Scott VN, Wiedmann M, Collette R, Jahncke ML, and Gall K. 2005. Guidelines for Listeria Testing of Environmental, Raw Product and Finished Product Samples in Smoked Seafood Processing Facilities. Food Protection Trends 25 (1): 23-24.
11. Lou Y, and Yousef AE. 1999. Characteristics of Listeria monocytogenes important to food processors. In Listeria, Listeriosis, and Food Safety, eds ET Ryser and EH Marth, 131-224. New York: Marcel Dekker, Inc. Available in Docket No. 1999N-1168, Volume 0014 bkg1 (11 of 17), Tab 245.
12. Institute of Food Technologists. 2001. Evaluation and Definition of Potentially Hazardous Foods. IFT/FDA Contract No. 223-98-2333.
13. Slutsker L, and Schuchat A. 1999. Listeriosis in humans. In Listeria, Listeriosis and Food Safety, eds ET Ryser and EH Marth, 75-95. New York: Marcel Dekker, Inc. Available in Docket No. 1999N-1168, Volume 0018 bkg1 (15 of 17), Tab 389.
14. Barnes R, Archer P, Strack J, Istre GR, and Centers for Disease Control and Prevention. 1989. Epidemiologic notes and reports listeriosis associated with consumption of turkey franks. Morbidity and Mortality Weekly Report 38: 267-268. Available in Docket No. 1999N-1168, Volume 0007 bkg1 (04 of 17), Tab 21.
15. Shank FR, Elliot EL, Wachsmuth IK, and Losikoff ME. 1996. US position on Listeria monocytogenes in foods. Food Control 7 (4-5): 229-234. Available in Docket No. 1999N-1168, Volume 0018 bkg1 (15 of 17), Tab 374.
16. Sorrells KM, Enigl DC, and Hatfield JR. 1989. Effect of pH, Acidulant, Time, and Temperature on the Growth and Survival of Listeria monocytogenes. Journal of Food Protection 52 (8): 571-573.
17. Petran RL, and Zottola.E.A. 1989. A Study of Factors Affecting Growth and Recovery of Listeria monocytogenes Scott A. Journal of Food Science 54 (2): 45-460.
18. Tienungoon S, Ratkowsky DA, McMeekin TA, and Ross T. 2000. Growth limits of Listeria monocytogenes as a function of temperature, pH, NaCl, and lactic acid. Applied and Environmental Microbiology 66 (11): 4979-4987.
19. Leistner L. 1995. Principles and applications of hurdle technology. In New Methods of Food Preservation, ed GW Gould, 1-21. London: Blackie Academic & Professional.
20. Scott VN, Swanson KMJ, Freier TA, Pruett WP, Sveum WH, Hall PA, Smoot LA, and Brown DG. 2005. Guidelines for Conducting Listeria monocytogenes Challenge Testing of Foods. Food Protection Trends 25 (11): 818-825.
21. Doyle ME, Mazzotta AS, Wang T, Wiseman DW, and Scott VN. 2001. Heat resistance of Listeria monocytogenes. Journal of Food Protection 64 (3): 410-429.
22. U.S. Food and Drug Administration. 2003. Chapter 10. Listeria monocytogenes. Detection and Enumeration of Listeria monocytogenes in Foods. In Bacteriological Analytical Manual Online.

• Appendix 1. Schematics Relevant to Recommended Plant Design
• Appendix 2. Recommended Schedules for Routine Cleaning and Sanitizing
• Appendix 3. Recommended Procedures for Collecting Environmental Samples
• Appendix 4. Recommended Procedures for preparing environmental samples for analysis

Laboratory analysis of samples should only be conducted by persons with appropriate microbiological training or experience. Listeria monocytogenes infection can cause serious illness and death, including fetal death. We recommend that pregnant women and persons who are immunocompromised because of illness, medication, or advanced age avoid working with this organism. Contaminated equipment and media should be sterilized before disposal or reuse.

1. Reagents, supplies, and equipment
   • Gloves (sterile)
   • Scissors (sterile)
   • Plastic bags (sterile) (e.g., Stomacher bag, Whirl-Pak®, or equivalent)
   • Pipettes (sterile) and 10 ml pipetting device
   • Vortex (or similar device for agitating)
   • Bottles with lids to hold 100 ml (sterile)
   • Tubes with lids (sterile) to hold 10 ml
   • Microbiological filters, 25-50 mm diameter (1-2 inches), 0.45 micron pore-diameter
   • Pre-filter - if there is a need to remove large particulates, use a pre-filter that is more coarse than the filters (e.g., sterile glass wool or cheesecloth with a diameter of 6.4 cm (2.5 inches)
     • Disposable filter/funnel units may be useful
   • Microbiological filter holder, water trap, water-driven air pump
   • Scalpels (sterile or capable of being flame-sterilized with 70% v/v ethanol)
   • Forceps/tweezers (sterile or capable of being flame-sterilized with 70 % v/v ethanol)
   • Ethanol solution, aqueous, 70% v/v (for flame sterilizing equipment such as forceps and scalpels)
   • Dey-Engley (D/E) neutralizing broth (Commercially available, or prepared according to the formula below)
     • Tryptone, 5 g
     • Yeast extract, 2.5 g
     • Dextrose (glucose) 10.0 g
     • Sodium thioglycollate, 1.0 g
     • Sodium thiosulfate, 6.0 g
     • Sodium bisulfite, 2.5 g
     • Polysorbate 80, 5.0 g
     • Lecithin (soy bean), 7.0 g
     • Bromcresol purple, 0.02 g
     • Distilled water 1.0 L
     • Final pH 7.6 ± 0.2 at 25 degrees C (77 degrees F)
   • Buffered Listeria Enrichment Broth base (BLEB) (includes sodium pyruvate) (see FDA's BAM, Chapter 10, M52)
   • Stomacher or sterile blender
2. Samples collected from sponges or swabs (Composite)

   A common technique we recommend is to combine analytical portions from several samples and analyze the mixture of the portions (which is referred to as a "composite"). If there is a positive result from the composite, the analysis could be repeated for reserve analytical portions from each individual sample that was combined to form the composite.

   To prepare a 5-sponge composite, squeeze or press liquid broth from the sponges from each of the 5 samples. Massage, blend, or stomach for 2 minutes. For each sample, pipette 5 ml of the broth into a sterile tube with lid, and retain it at 5 degrees C (41 degrees F) as a reserve for analysis if the composite is positive for Listeria species. Combine the remaining portions of each sample, including the sponges, to form the composite that will be used for analysis. With sterile forceps remove each of the 5 sponges and place into 225 ml of BLEB.

   To prepare a 5-swab composite, shake and then press the liquid from the swab for each sample. Pipette 5 ml of broth into a sterile tube with lid for each sample, and retain it at 5 degrees C (41 degrees F) as a reserve for analysis if the composite is positive for Listeria species. Combine the remaining portions of each sample, including the swabs, to form the composite that will be used for the analysis.

   If you homogenize using a Stomacher, add 225 ml of BLEB to the individual or composited sponges/swab tips in transport fluid in a sterile plastic bag suitable for use in a Stomacher. Place in the Stomacher for 2 minutes. If you use a blender, add 225 ml of BLEB to the individual or composited sponges/swab tips and transport fluid in sterile blender jar. Blend for 2 minutes.

3. Samples collected from liquids

   We recommend that as soon as possible after sample collection, you filter 100 ml of the collected liquid through one or more sterile 0.45 micron pore-diameter filters. If particulate content is high (e.g., judging from the sample turbidity), we recommend that you pass the liquid through a sterile glass pre-filter before the 0.45 micron filter. Rinse the retentate on the filter plus any pre-filter with 5-10 ml of D/E broth to remove any residual inhibitory substances. If necessary, excise the filters from the funnel devices, using sterile scalpels. Put each filter and the pre-filter, if any, in a sterile bag (if you will use a Stomacher) or in a sterile container (such as a blender jar, if you use a blender).

   Note: If composites are made from the filters, cut filter and any pre-filter in half using sterile instruments. Use one half of each filter to form a composite and retain the other half at 5 degrees C (41 degrees F) as a reserve for analysis if the composite is positive for Listeria species.

   Add 225 ml of BLEB to the individual or composited filters/pre-filters. Stomach or blend for 2 minutes.

We recommend that you incubate the analytical portions prepared in BLEB at 30 degrees C (86 degrees F) for 4.0 hours to pre-enrich for Listeria species. We also recommend that you then add the selective agents, i.e., acriflavin, sodium nalidixate, and cycloheximide (BAM; M52), and continue incubating at 30 degrees C (86 degrees F) for another 20.0 hours for a total incubation time of 24 hours. If using FDA's BAM, the applicable section for you to refer to is Section D. Isolation procedure.

Figure 1 is a graphic representation showing that the recommended air flow should have negative pressure in the raw processing area rather than in the RTE processing area.

Figure 2 is one of two figures with schematic representations showing examples of plant design, including schematic representations related to recommendations for air flow, product flow and the use of partitions in the design of the plant. In Figure 2, the raw processing area is separated from the RTE processing area by a partition. This differs from Figure 3, in which there is no partition, but there is additional positive air pressure in the RTE processing area. The rest of both figures show recommendations to:

• Place partitions between:
  • The office area and the raw processing area;
  • Areas designated for receiving raw materials, storing raw materials, processing raw foods, and the in-process cooler;
  • The raw processing area and the area designated for cleaning equipment used in processing raw foods;
  • The raw processing area and a vestibule separating that area from rest rooms and locker rooms designated for use by employees when they work in the raw processing area;
  • The in-process cooler and the RTE processing area;
  • The RTE processing area and the area designated for cleaning equipment used in processing RTE foods;
  • The RTE processing area and a vestibule separating that area from rest rooms and locker rooms for use by employees when they work in the RTE processing area;
  • The RTE processing area and the finished product storage area;
  • The finished product storage area and the finished product shipping area; and
  • Locker rooms and a break room.
• Place doorways between:
  • The outside and the office area;
  • The outside and the area designated for receiving raw materials;
  • The areas designated for receiving and storing raw materials;
  • The office area and the raw processing area;
  • The raw processing area and the areas designated for receiving raw materials, storing raw materials, and cleaning equipment used in processing raw foods;
  • The raw processing area and a vestibule leading to the rest rooms and locker rooms for use by employees when they work in the raw processing area;
  • The RTE processing area and the in-process cooler;
  • The RTE processing area and the areas designated for cleaning equipment used in the processing of RTE foods and for storing finished product;
  • The RTE processing area and the vestibule leading to the rest rooms and locker rooms for use by employees when they work in the RTE processing area;
  • The finished product storage area and the finished product shipping area;
  • The finished product shipping area and the outside; and
  • Locker rooms and a break room.
• Place the product cooker so that it spans the raw processing area and the RTE processing area and can be opened in both areas;
• Place hand washing stations:
  • In the RTE processing area at the entrance to the raw processing area, the in-process cooler, the area designated for cleaning equipment used to process RTE foods, the area designated for finished product storage, and the vestibule leading to rest rooms and locker rooms; and
  • In the vestibules leading to rest rooms and locker rooms.
• Place footbaths in the RTE processing area at:
  • The entrance to the raw processing area;
  • The entrance to the finished product storage area; and
  • The vestibule leading to the rest rooms and locker rooms.
• Provide for equipment decontamination in the RTE processing area at:
  • The entrance to the raw processing area; and
  • The finished product storage area.
• Provide positive air pressure:
  • In the office area near the entrance to the raw processing area;
  • In the raw processing area near the entrance to the RTE processing area;
  • In the raw material receiving area near the entrance to the raw processing area;
  • In the raw material storage area near the entrance to the raw processing area;
  • In the area designated for cleaning equipment used to process raw foods near the entrance to the raw processing area;
  • In the in-process cooler near the entrance to the RTE processing area;
  • In the finished product storage area near the entrance to the RTE processing area;
  • In the finished product shipping area near the entrance to the finished product storage area;
  • In the area designated for cleaning equipment used to process RTE foods near the entrance to the RTE processing area;
  • In the rest rooms near the entrance to the vestibule; and
  • In the locker rooms near the entrance to the vestibule.

Figure 3 is one of two figures with schematic representations showing examples of plant design, including schematic representations related to recommendations for air flow, product flow and the use of partitions in the design of the plant. Figure 3 shows additional positive air pressure at the juxtaposition between the RTE processing area and the raw processing area relative to the amount of positive air pressure in Figure 2, where the raw processing area is separated from the RTE processing area by a partition. The remaining recommendations in Figure 3 are the same as those in Figure 2.