Submitted to: Zoonoses and Public Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2009
Publication Date: 5/1/2010
Citation: Bhaduri, S., Phillips, J.G. 2010. GROWTH MODEL OF A PLASMID-BEARING VIRULENT STRAIN OF YERSINIA PSEUDOTUBERCULOSIS IN RAW GROUND BEEF. Zoonoses and Public Health. DOI: 10.1111/j.1863-2378.2009.01271. Interpretive Summary: Yersinia pseudotuberculosis (YPT) is recognized as an important causal agent of sporadic and epidemic human enteric disease and has a wide distribution in both wild and domestic animals. The chromosomal DNA sequence of Y. pestis and YP are nearly identical. Since YP is also a foodborne pathogen; it can be used as a model organism for Y. pestis. Risk assessors are interested in knowing the growth of Y. pestis in ground beef, since that would threaten the health of a large number of individuals. Hence, the growth of YP was modeled in sterile raw ground beef from 0 to 30 degree C. The YP grew at storage temperatures from 0 to 25 degree C, but the growth rate was reduced at 30 degree C. Models were produced for YP growth rate and maximum population density, and shown to have excellent prediction. The growth of YP was not inhibited in retail ground beef containing native microflora. The virulence-ability was retained in YP during its growth in ground beef and, therefore, raw ground beef contaminated with YP could cause disease if the ground beef was not properly cooked. The model developed can be used for as a reference for Y. pestis growth in ground beef and therefore, ensure safety of the food.
Technical Abstract: The growth kinetics of Yersinia pseudotuberculosis (YPT) in sterile ground beef were studied at temperatures ranging from 0 to 30 C. In irradiated sterile ground beef, YP replicated from 0 to 30 degree C, with corresponding growth rates (GR) ranging from 0.0227 to 0.6221 log10 CFU/h at 0 to 25 degree C, and the GR was 0.2360 log CFU/h at 30 degree C. The maximum population densities (MPD) (P>0.005) ranged from 8.7 to 11.0 log CFU/g. The growth and MPD of YP were reduced significantly at 30 degree C. Models for growth rate and MPD of YP in RGB as a function of storage temperatures were produced and shown to have possessed good bias and accuracy. The models were validated with rifampicin resistant YP (rif-YP) in sterile ground beef stored at 4, 10, and 25 degree C. The observed growth rate and MPD were within 95% of the predicted values. When compared to non-sterile retail ground beef, the growth of rif-YP was not inhibited and displayed the same growth rates at 0, 10, and 25 degree C and MPDs as it did in sterile ground beef at 10 and 25 degree C. The virulence-associated plasmid was retained in YP during its growth in ground beef indicating that raw ground beef contaminated with YP could cause disease if the meat was not properly cooked.