ESCHERICHIA-COLI O157-H7 ACID TOLERANCE AND SURVIVAL IN APPLE CIDER

The survival of two Escherichia coli 0157:H7 (ATCC 43889 and 43895) an d a control strain E coli was compared in apple cider and in Trypticas e soy broth (TSB) adjusted to low and high pH. The 0157:H7 strains wer e detectable in apple cider after 14 to 21 days at 4-degrees-C, wherea s the control strain could not be detected (> 4-log reduction) after 5 to 7 days. During the first 14 days of storage at 4-degrees-C, the le vels of strain 43889 decreased by approximately 3 logs, whereas levels of strain 43895 were unchanged. Survival of 0157:H7 strains and the c ontrol strain were unaffected by the presence of potassium sorbate or sodium benzoate, except in one instance. Sodium benzoate caused a decr ease of 57% in strain 43895 after 21 days, but approximately 10(4) CFU /ml still remained. In TSB adjusted to pH 2, 3, 4, 11 or 12, strain 43 895 was again the more resistant of the 0 1 57:H7 strains, both of whi ch were more durable than the control strain. The 0157:H7 strains (esp ecially strain 43895) withstood pH 2 with a minimal drop in CFU after 24 h, whereas no viable organisms were detectable after this time at p H 12. At these extremes of pH, survival was generally greater at 4-deg rees-C than at 25-degrees-C. Despite differences between strains, thes e results show that E coli 0157:H7 is exceptionally tolerant of acid p H.