Storage and holding
temperature also affect heat resistance of E. coli O157: H7. Cultures frozen at-18 C showed greater heat resistance in a nutrient medium and in ground beef patties than those stored under refrigeration (3 oC) or 15 C, probably due to physiological changes within the bacterial cell that were caused by freezing (Jackson and others. 1996). Exposure of non- heat-shocked cells of E. coli to 0 C before heating significantly increased the heat sensitivity of the exposed cells (Katsui and oth ers 1982). On the other hand, Juneja and others (1998) reported that the heat resistance of non-heat-shocked E. coli storage cells inoculated into ground beef was not changed after at 4 C for 48 h.