Changes in Heat Resistance of Escherichia coli O157:H7 Following Heat Shock

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Abstract
This study examined the effects of a heat shock at 45°C for 30 min on the subsequent heat resistance of Escherichia coli O157:H7 ATCC 43894 in Trypticase soy broth (TSB) and ground beef slurry (GBS). Cultures were grown to stationary phase, stored for 24 h at 4 to 6°C, and then heat shocked to simulate consumer mishandling of meat during the summer. Control or heat-shocked ATCC 43894 cells were then transferred to prewarmed TSB (54, 58, and 62°C) or GBS (58°C) and refrigerated TSB and GBS that were subsequently heated to and held at 58°C (TSB and GBS) and 62°C (TSB only). Heat shock increased D values by 37, 68, and 50% in 54, 58, and 62°C prewarmed TSB, respectively, but had no significant effect on the D value in 58°C GBS. Immediate plating of heated samples yielded greater cell recovery than if samples were held on ice prior to plating. Heat shock did not lead to significant increases in D values when cells were transferred to 4°C TSB and GBS that were heated to the test temperature. This study showed ...

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