Title: Effect of fat in ground beef on the growth and virulence plasmid (pYV) stability in Yersinia pestis Author
Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 28, 2009
Publication Date: January 1, 2010
Citation: Bhaduri, S. 2010. Effect of fat in ground beef on the growth and virulence plasmid (pYV) stability in Yersinia pestis. International Journal of Food Microbiology. 136:372-375. Interpretive Summary: Yersinia pestis (YP) is the causative agent of bubonic plague in humans. Although there are few reports of its role in foodborne outbreaks, there is a concern that it could be a biosecurity threat, potentially leading to significant morbidity and mortality. Risk assessors are interested in knowing the fate of YP in food, since contaminated food would threaten the health of large number of individuals. Thus, we have investigated the growth of a strain of YP in raw ground beef (RGB) with different fat content over a range of temperatures. The YP grew normally at storage temperatures of 10 and 25 degrees C. The YP did not grow at 0 and 4 degrees C but survived. We also found that YP in refrigerated RGB retained its virulence ability. This information supports the need of proper cooking of RGB.
Technical Abstract: Knowledge of the behavior of Yersinia pestis in food may be useful in the event Y. pestis is used in a bioterrorism attack on the food supply. However, there are no reports on the growth of plasmid-bearing (pYV) virulent Y. pestis in food. The growth of a conditionally virulent pYV-bearing Yersinia pestis KIM5 (KIM5) in sterile raw ground beef (RGB) with 7, 15 and 25% fat content was studied at 0, 4, 10 and 25 degrees C. The KIM5 did not grow but survived in RGB at 0 and 4 degrees C. In RGB with fat contents of 7, 15 and 25% KIM5 replicated at 10 degrees C with growth rates of 0.057, 0.0501, and 0.055 log10 CFU/h and maximum population density (MPD) of 8.65, 8.30, and 8.43 log10 CFU/g, respectively. The growth rate was 4-fold higher and the MPD was slightly higher at 25 degrees C in RGB at all levels of fat as compared to 10 degrees C. Moreover, there was no loss of pYV in surviving KIM5 in RGB stored at refrigerator temperatures or during its growth in RGB. This suggests that RGB contaminated with virulent Y. pestis could cause oro-pharyngeal plague due to refrigeration failure, temperature (10-25 degrees C) abuse, and if the meat was not properly cooked.