The survival of two Escherichia coli O157:H7 (ATCC 43889 and 43895) and a control strain E. coli was compared in apple cider and in Trypticase soy broth (TSB) adjusted to low and high pH. The O157:H7 strains were detectable in apple cider after 14 to 21 days at 4°C,
whereas the control strain could not be detected (> 4-log reduction) after 5 to 7 days. During the first 14 days of storage at 4°C, the levels of strain 43889 decreased by ∼3 logs, whereas levels of strain 43895 were unchanged. Survival of O157:H7 strains and the control strain
were unaffected by the presence of potassium sorbate or sodium benzoate, except in one instance. Sodium benzoate caused a decrease of 57% in strain 43895 after 21 days, but ∼104 CFU/ml still remained. In TSB adjusted to pH 2, 3, 4, 11 or 12, strain 43895 was again the more resistant
of the O157:H7 strains, both of which were more durable than the control strain. The O157:H7 strains (especially strain 43895) withstood pH 2 with a minimal drop in CFU after 24 h, whereas no viable organisms were detectable after this time at pH 12. At these extremes of pH, survival was generally
greater at 4°C than at 25°C. Despite differences between strains, these results show that E. coli O157:H7 is exceptionally tolerant of acid pH.
Food Research Institute, University of Wisconsin - Madison, 1925 Willow Drive, Madison, Wisconsin 53706
Publication date: June 1, 1994
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