BEHAVIOR OF YERSINIA PESTIS STRAINS KIM5 AND CDC A1122 IN RAW GROUND BEEF

Authors: Bhaduri, Saumya; Tamplin, Mark

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/30/2006
Publication Date: 10/10/2006
Citation: Bhaduri, S., Tamplin, M.L. 2006. Behavior of yersinia pestis strains kim5 and cdc a1122 in raw ground beef. Meeting Abstract.

Interpretive Summary:

Technical Abstract: Although Yersinia pestis, the causative agent of bubonic and pneumonic plague, has not been implicated in a foodborne outbreak, there is ongoing concern about the potential use of this pathogen as a foodborne biological weapon. There are no reports of the behavior of Y. pestis in food, and hence little understanding about the consequences of intentional food contamination. Hence, the growth kinetics and inactivation of Y. pestis KIM5 in sterile and non-sterile ground beef were investigated at storage temperatures ranging from lower (-20oC) to upper (43oC) to define growth regions and the minimum and maximum temperatures that support Y. pestis growth. Ninety-gram portions of ground beef were artificially contaminated with Y. pestis KIM5 at a concentration of 105 CFU/g for growth kinetics and at a concentration 108 CFU/g for inactivation at freezing temperatures. Samples were weighed into 3-gram portions and were stored at temperatures ranging from -20oC to 43oC. At various time intervals, samples were serially diluted, surface plated onto Congo red magnesium oxalate agar, incubated at 37oC for 48 hour and enumerated. For non-sterile ground beef studies, rifampicin (rif)-resistant isolates of KIM5 were produced and colonies enumerated on tryptic soy agar containing 100 ug/ml rif. In sterile ground beef, Y. pestis KIM5 were incubated at temperatures from 0 to 40 deg. C; corresponding growth rates ranged from 0.0014 to 0.2887 CFU/h and maximum population densities (MPD) from 7.4 to 9.8 CFU/g. In contrast, Y. pestis KIM5 in nonsterile ground beef was inactivated at -20 deg. C and at temperatures greater than or equal to 41 deg. C. Y. pestis strain CDC A1122 displayed both lower growth rates and MPDs at 10, 25 and 37 deg. C compared to KIM5. Models for Y. pestis KIM5 growth rates and MPDs were produced and shown to possess good bias and accuracy. In two different batches of non-sterile retail ground beef containing native microflora, the growth of a cocktail of three rif-resistant Y. pestis KIM5 isolates was markedly inhibited. The virulence-associated plasmid pCD/pYV was lost from Y. pestis KIM5 during ground beef storage.