EFFECT OF HEAT-SHOCK AND INCUBATION ATMOSPHERE ON INJURY AND RECOVERYOF ESCHERICHIA-COLI O157-H7

Escherichia coli serotype O157:H7 cells were grown at 30-degrees-C for 6 h and subjected to a heat stress, or heat shock, at 42-degrees-C fo r 5 min. Heat-shocked and nonheat-shocked controls were heat treated a t 55-degrees-C for up to 60 min. The number of injured cells was signi ficantly higher in heat-shocked cells than in controls, and the rate o f release of cell components was higher in heat-shocked cells. Anaerob ic plating resulted in higher recovery of injured cells, when compared with aerobic plating, regardless of whether the cells were heat shock ed or not. In addition, heat shocking resulted in lower catalase and s uperoxide dismutase activities when compared with controls. It also re sulted in greater survivability after exposure to hydrogen peroxide, s uggesting that heat shocking somehow enables the cells to survive expo sure to toxic substances in addition to heat. The heat-shock response, coupled with anaerobic conditions, increased the ability of E. coli O 157:H7 cells to recover after a heat treatment. Thus, heat shock did n ot afford protection to the cells against injury, but rather enhanced their ability to recover during storage.