Survival, injury, and virulence of freeze-stressed plasmid-bearing virulent Yersinia enterocolitica in ground pork

The effect of freezing at -20 degrees C on survival, injury, stability of the virulence plasmid, and expression of virulence-associated determinants of Yersinia enterocolitica (YEP+) in ground pork was assessed. The viable counts on nonselective and selective media after 12 weeks of freezing were similar to counts obtained before freezing, indicating that the YEP+ strain survived the freezing process. There was no evidence of freeze-stress injury. Results of a PCR assay targeting plasmid-associated virF gene and virulence determinants indicate that YEP+ subjected to freezing are potentially capable of causing food-borne illness and freezing is not a substitute for safe handling and proper cooking of pork.