This study investigated the effects of heat shock and post-heat environmental conditions on the survival of Escherichia coli ATCC 25922 at 52, 54 and 56°C. Significantly (P <0.05) higher decimal reduction time-values (D-values) in nutrient broth at all three temperatures were obtained when the cells had been previously heat shocked at 46°C for 1 h. This heat shock effect was greatest at 56°C, followed by 54 and 52°C. Anaerobic jar incubation of heat-stressed cells led to D-values higher than those obtained using aerobic incubation, but the difference was only statistically significant at 56°C. Previous studies showed that fluid thioglycollate medium and thioglycollic acid enhanced the recovery of heat-stressed Salmonella enteritidis and E. coli, respectively. However, a fluid thioglycollate medium overlay of spread plates significantly decreased the D-values of E. coli ATCC 25922 at 52, 54 and 56°C. When the fluid thioglycollate medium was used to overlay pour plates, no significant changes in D-values were seen.

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