Growth Model of a Plasmid-Bearing Virulent Strain of Yersinia pseudotuberculosis in Raw Ground Beef

Summary The growth kinetics of virulence plasmid-bearing Yersinia pseudotuberculosis (YPST) in sterile ground beef were studied at temperatures ranging from 0 to 30°C. In irradiated sterile ground beef, YPST replicated from 0 to 30°C, with corresponding growth rates (GR) ranging from 0.023 to 0.622 log CFU/h at 0–25°C, and the GR was 0.236 log CFU/h at 30°C. The maximum population densities (MPD) ranged from 8.7 to 11.0 log CFU/g. The growth and MPD of YPST were reduced significantly at 30°C. Models for GR and MPD of YPST in raw ground beef (RGB) as a function of storage temperatures were produced and displayed acceptable bias and accuracy. The models were validated with rifampicin-resistant YPST (rif-YPST) in sterile ground beef stored at 4, 10 and 25°C. The observed GR and MPD were within 95% of the predicted values. When compared to non-sterile retail ground beef, the growth of rif-YPST was not inhibited and displayed similar GR at 0, 10 and 25°C and MPDs as sterile ground beef at 10 and 25°C. Moreover, there was no loss of virulence plasmid in YPST during its growth in ground beef indicating that RGB contaminated with virulence plasmid-bearing YPST could cause disease due to refrigeration failure, temperature (10–25°C) abuse, and if the meat was not properly cooked.