EFFECT OF HEAT-SHOCK ON THE THERMOTOLERANCE AND PROTEIN-COMPOSITION OF YERSINIA-ENTEROCOLITICA IN BRAIN HEART INFUSION BROTH AND GROUND PORK

The optimum conditions required to induce a heat-shock response in Yer sinia enterocolitica in brain heart infusion (BHI) broth were determin ed. The production of heat-shock proteins and the increased thermotole rance of heat-shocked Yersinia cells in ground pork when exposed to hi gher temperatures was also examined. Heat shocking Y. enterocolitica c ells at 45 degrees C for 60 min consistently resulted in an increased number of survivors to a subsequent treatment of 55 or 60 degrees C in BHI broth when compared with non-heat-shocked controls. D values at 5 5 degrees C were calculated as 7.7 and 2.0 min and at 60 degrees C as 1.6 and 1.2 min for heat-shocked and control cells, respectively. Afte r examination of heat-shocked cells by sodium dodecyl sulfate-polyacri lamide gel electrophoresis (SDS-PAGE), two distinct heat-shock protein s with molecular masses of 70.5 and 58.0 kDa were observed that were n ot present in the control. Evaluation of heat-shocked and control cell survival in ground pork revealed D-55 values of 15.6 and 6.5 min and D-60 values of 6.7 and 1.7 min, respectively. The results indicate tha t prior heat shock can induce increased resistance in Y. enterocolitic a in ground pork to higher heat treatments. Survival of Yersinia enter ocolitica in cooked meat due to the phenomenon of the heat-shock respo nse can become a cause of concern regarding microbiological food safet y.