Effect of Heat Shock on the Thermotolerance and Protein Composition of Yersinia enterocolitica in Brain Heart Infusion Broth and Ground Pork.

Abstract

The optimum conditions required to induce a heat-shock response in Yersinia enterocolitica in brain heart infusion (BHI) broth were determined. The production of heat-shock proteins and the increased thermotolerance of heat-shocked Yersinia cells in ground pork when exposed to higher temperatures was also examined. Heat shocking Y. enterocolitica cells at 45°C for 60 min consistently resulted in an increased number of survivors to a subsequent treatment of 55 or 60°C in BHI broth when compared with non-heat-shocked controls. D values at 55°C were calculated as 7.7 and 2.0 min and at 60°C as 1.6 and 1.2 min for heat-shocked and control cells, respectively. After examination of heat-shocked cells by sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE), two distinct heat-shock proteins with molecular masses of 70.5 and 58.0 kDa were observed that were not present in the control. Evaluation of heat-shocked and control cell survival in ground pork revealed D55 values of 15.6 and 6.5 min and D60 values of 6.7 and 1.7 min, respectively. The results indicate that prior heat shock can induce increased resistance in Y. enterocolitica in ground pork to higher heat treatments. Survival of Yersinia enterocolitica in cooked meat due to the phenomenon of the heat-shock response can become a cause of concern regarding microbiological food safety.