Log phase cells of Escherichia coli 0157:H7 were grown aerobically at 30°C and heat shocked at various time/temperature combinations to determine the optimum conditions that would result in the highest number of survivors to a subsequent 55°C heat treatment. Heat shocking at 42°C for 5 min resulted in the largest increase in D55 value over nonheat-shocked controls of all heat-shock time/temperature combinations tested. Growth atmosphere significantly contributed to the heat resistance of both heat-shocked and nonheat-shocked cells, with anaerobically grown cells having D55 values higher than those of cells grown aerobically. Therefore, both heat shocking and anaerobic growth contributed to an increase in the number of survivors of E. coli 0157:H7 cells when compared with nonheat-shocked cells grown aerobically. Aerobically grown, heat-shocked cells, and anaerobically grown cells, both heat-shocked and nonheat-shocked, contained a 71,000 dalton protein not present in aerobically grown, nonheat-shocked controls. This protein was found to be immunologically similar to a sigma32 subunit of RNA polymerase, as evidenced by Western Blot using monoclonal antibodies specific for the sigma subunit. In addition to heat, anaerobic growth appeared to be a form of stress, since it resulted in the synthesis of heat-shock proteins and in an increased survival of cells to a heat treatment.
1Present address: Dept. of Microbiology, Immunology & Preventive Medicine, Iowa State University, 382 Science 1, Ames, Iowa 50010.