Thermotolerance of Listeria monocytogenes and Salmonella typhimurium after sublethal heat shock.

The effect of prior heat shock on thermotolerance of Listeria monocytogenes and Salmonella typhimurium in broth culture was determined. Bacteria were grown at the permissive temperature of 35 degrees C, sublethally heated at 35 (control), 42, 48, and 52 degrees C (nonpermissive control) for various times, and inactivated at either 57.8 or 52 degrees C. The induction of increased thermotolerance by heat shock, although consistent within each experiment, was generally not significant for L. monocytogenes; the increase was significant for S. typhimurium. Temperature shift experiments with L. monocytogenes suggested that induced thermotolerance was not long lived unless the shock temperature was maintained.