Three strains of Escherichia coli 0157:H7 (ATCC 43895, Ent C9490 and 380-94) were inoculated into salami and heated in water baths at 50, 55 or 60 deg C. At intervals between I and 360 min, salami samples were removed from the water bath and examined for the presence of surviving E. coli 0157:H7. Samples were directly plated onto sorbitol MacConkey (SMAC) agar, and onto tryptone soya agar (TSA) with SMAC overlay. The number of sub-lethally damaged cells in each sample was estimated from the differences between the resultant direct (uninjured cells only) and overlay (total recovery) counts. In samples heated at 50 deg C, the percentage of cell injury ranged from 71.8-88 for all strains. In samples heated at 55 deg C the percentage of sub-lethally damaged cells in strains A TCC 43895 and Ent C9490 was significantly higher (P < 0.001) at 97 than that observed in strain 380-94 (64). Cell injury was not measured at 60 deg C. There were significant differences between the derived decimal reduction times (D-values) related to the different strains of E. coli 0157:H7, the heat treatment applied and the recovery/enumeration agars used. Significant interstrain differences (P < 0.05) in thermotolerance were noted. Strain Ent C9490 was significantly more heat resistant at 50 deg C and 60 deg C (D-values of 116.9 and 2.2 min, respectively), while at 55 deg C strain 380-94 was more thermotolerant (D-value of 21.9 min). The implications of these findings for the design of studies investigating the heat resistance of E. coli 0157:H7 in fermented meat environments are discussed.
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