The Effect of Acid Adaptation Conditions on Acid Tolerance Response of Escherichia coli O157: H7

This study examined the effects of acid shock and acid adaptation on acid tolerance of E. coli O157: H7 932 strain. E.coli O157: H7 were exposed to acid at pH 4.5, 5.0 or 5.5 for acid adaptation or acid shock in tryptic soy broth (acidified with 6 NHCI). Acid shocked cells were incubated for 1, 2, 3 or 4 h while acid adapted cells were incubated for 18 h at 37¡C and then acid tolerance of acid shocked and acid adapted cells were determined by exposing to acid challenge of pH 2.5 or 3.0 in tryptic soy broth.Acid shocked, acid adapted and control cells were incubated at 37¡C and survival of the cells at 0, 2, 4, 6, 7, 24 and 48 h was determined.Acid shock increased acid tolerance of E. coli O157: H7 at pH 3.0. However, acid tolerance was not induced in acid adapted cells ateither pH 2.5 or 3.0. Acid shocked cells exposed to acid at pH 4.5 for 2 h had the highest acid tolerance (P 0.05).The results indicated that exposure to acidic environments (pH 4.5- 5.5) for a short time increased acid tolerance of E. coli O157:H7. Acid shocked cells of E. coli O157: H7 may be considered in fermented foods, fruit juices and for acid spray process in the meatindustry.