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National Shellfish Sanitation Program
U.S. Food and Drug Administration
Shellfish Safety Team
Division of Cooperative Programs
Office of Compliance
Model Ordinance Chapter XV.03.L.(1)(c)
Reference: NSSP Guidance Documents
Approved NSSP Laboratory Tests
Key Words: Sample Volume, Fecal Coliform Counts,
MPN Table and Count Range
Question: | What sample volume is inoculated in
the 12-tube, single dilution MPN test for end product depurated
shellfish samples? How are fecal coliform counts determined using the 12-tube, single dilution MPN test for end product depurated shellfish? |
MPN Table for End-product Depurated Shellfish Samples | |
---|---|
Number of Positive Tubes | MPN/100 grams |
0 |
< 9.0 |
1 |
9.0 |
2 |
18 |
3 |
29 |
4 |
41 |
5 |
54 |
6 |
70 |
7 |
88 |
8 |
110 |
9 |
139 |
10 |
179 |
11 |
248 |
12 |
>248 |
Count range 9 to 248 |
Rationale:
The use of the 12-tube, single dilution MPN test for end-product depurated shellfish was established as an acceptable method of analysis with the ISSC's adoption of the rewrite of Model Ordinance, Chapter XV, the Depuration Chapter in 1998. However, no specific guidance was provided on sample volumes to be examined or how fecal coliform counts were to be determined. Since the volume of sample inoculated in a single dilution MPN test controls the range of counts that can be determined, it is essential that an appropriate volume be inoculated to encompass the count range prescribed as the critical limits for depuration plant performance listed for all shellfish species encountered.
The inoculation of two (2) ml (yielding 1 gram) of sample from an
initial 1:1 dilution of shellfish homogenate into each tube of the
12-tube, single dilution MPN produces a range of counts from 9 to 248.
This range is sufficient to cover the critical limits of performance of
all shellfish types listed in Chapter XV.03.L(1)(c).
Remarks:
Comments received from the review of the draft version of Interpretation 03-XV-.03-100 indicated that the content of the Interpretation was too broad to be dealt with effectively in a single Interpretation. For this reason, this second Interpretation was developed from information presented in the first concerning the correct application of the single dilution MPN test to end product depurated shellfish.
Contact:
U.S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
5100 Paint Branch Parkway (HFS-628)
College Park, MD 20740
Shellfish Specialists
Regional Federal State Program Managers
Division of Federal State Relations
Office of Seafood
Interstate Shellfish Sanitation Conference