ARS | Publication request: Growth Model of a Plasmid-bearing Virulent Strain of Yersinia pseudotuberculosis in Raw Ground Beef

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: February 10, 2008
Publication Date: August 4, 2008
Citation: Bhaduri, S., Phillips, J.G. 2008. Growth Model of a Plasmid-bearing Virulent Strain of Yersinia pseudotuberculosis in Raw Ground Beef. Meeting Abstract. P5-04. page 153.

Technical Abstract: Introduction: Yersinia pseudotuberculosis (YPST) has been implicated in foodborne illnesses associated with various foods, including raw beef. A 70-kb virulence plasmid (pYV) is involved in expression of virulence phenotypes. However, increased growth temperatures (30 degree C) facilitate the loss of this plasmid and the virulence-associated determinants. Purpose: There are no reports concerning the growth of plasmid-bearing virulent YPST in raw ground beef (RGB). To fully assess the potential risk of illness, it is necessary to know the effect of the endogenous microflora on the behavior/fate of YPST in RGB. Method: Ninety-gram portions of retail RGB (~7% fat) either irradiated or raw were artificially contaminated with serotype O:1b YPST PB1/+ strain and rifampicin (rif)-resistant YPST PB1/+ strain (rif-YPST) at a concentration of 105 CFU/g. Samples (3-gram) were stored at temperatures ranging from 0-30 degree C. At various time intervals, samples were serially diluted in 1% peptone water, surface plated onto Congo red-(CR)-magnesium-oxalate agar (CRMOX), and then incubated at 37 degree C for 48 hours for enumeration and detection of pYV-YPST by CR binding. For non-sterile RGB studies, rif-YPST colonies were enumerated on rif-(100 µg/ml)-CRMOX. Results: In sterile RGB, the growth rate (GR) ranged from 0.0227 to 0.6221 log10 CFU/h at 0 to 25 degree C and maximum population densities (MPD) ranged from 8.7 to 11.0 log CFU/g. The GR and MPD models were developed as a function of storage temperature. The models were validated with rif-YPST in sterile RGB. In non-sterile RGB, rif-YPST displayed the similar GR and MPDs as in sterile RGB. This may be due to low level (4.31±0.60 log CFU/g) of background microflora in fresh retailed RGB. Significance: Models for GR and MPD of YPST in RGB displayed acceptable bias and accuracy within 95% of the predicted values. Moreover, there was eventually no loss pYV at the temperatures evaluated herein. Therefore, beef contaminated with YPST could cause disease if the meat was not properly cooked.