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United States Department of Agriculture

Agricultural Research Service


Location: Residue Chemistry and Predictive Microbiology

Title: Growth Model of a Plasmid-bearing Virulent Strain of Yersinia pseudotuberculosis in Raw Ground Beef

item Bhaduri, Saumya
item Phillips, John

Submitted to: Meeting Abstract
Publication Type: Abstract Only
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.

Last Modified: 4/17/2014
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