The objective of this study was to determine the effect of acid adaptation conditions on heat resistance of E. coli 0157: H7 932. E. coli 0157: H7 was adapted to acid by exposing the cells to pH 4.5 (2h), pH 5.0 (lh), and pH 5.5 (1h) in tryptic soy broth. D and z values of the acid adapted and control cultures at 54°C, 56°C, and 58°C were determined in E buffer. The heat resistance of E. coli 0157: H7 increased significantly (p<0.05) after acid adaptation at pH 4.5 or pH 5.0. E. coli 0157: H7 adapted to acid at pH 4.5 for 2 h had the highest D values at all temperatures tested (20.3-10.7-3.3 min) while D values of culture adapted to acid at pH 5.0 for 1h were 18.2, 7.9, and 2.6 min at 54°C, 56°C and 58°C, respectively. Heat resistance of culture adapted to acid at pH 5.5 for 1h and the control culture was not significantly different (P<0.05). Culture adapted to acid at pH 4.5 had the highest z value (5.10°C), whereas control culture had the lowest z value (4.33°C). This study showed that the magnitude of heat tolerance changed with the adaptation pH and at low adaptation pH, E. coli 0157: H7 showed maximum heat resistance. Acid adaptation at pH 4.5 or 5.0 provides E. coli 0157: H7 with cross-protection against heat treatments, and that this factor must be considered to estimate this pathogen's thermal tolerance accurately.
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