Effect of fat in ground beef on the growth and virulence plasmid (pYV) stability in Yersinia pestis.

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 Y. pestis KIM5 in sterile raw ground beef with 7, 15 and 25% fat content was studied at 0, 4, 10 and 25 degrees C. The Y. pestis KIM5 did not grow but survived in raw ground beef at 0 and 4 degrees C. In raw ground beef with fat contents of 7, 15 and 25% Y. pestis KIM5 replicated at 10 degrees C with growth rates of 0.06, 0.05, and 0.06 log(10) CFU/h and maximum population densities of 8.65, 8.30, and 8.43 log(10) CFU/g, respectively. The growth rate was 4-fold higher and the maximum population density was slightly higher at 25 degrees C in raw ground beef at all levels of fat as compared to 10 degrees C. Moreover, there was no loss of pYV in surviving Y. pestis KIM5 in raw ground beef stored at refrigerator temperatures or during its growth in raw ground beef. This suggests that raw ground beef 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. The resultant disease may lead to outbreaks of highly infectious pneumonic plague.