GROWTH AND SURVIVAL OF ESCHERICHIA-COLI O257-H7 UNDER ACIDIC CONDITIONS

The effect of pH reduction with acetic (pH 5.2), citric (pH 4.0), lact ic (pH 4.7), malic (pH 4.0), mandelic (pH 5.0), or tartaric (pH 4.1) a cid on growth and survival of Escherichia coli O157:H7 in tryptic soy broth with 0.6% yeast extract held at 25, 10, or 4 degrees C for 56 da ys was determined. Triplicate flasks were prepared for each acid treat ment at each temperature. At 25 degrees C, populations increased 2 to 4 log(10) CFU/ml in all treatments except that with mandelic acid, whe reas no growth occurred at 10 or 4 degrees C in any treatments except the control. However, at all sampling times, higher (P < 0.05) populat ions were recovered from treatments held at 4 degrees C than from thos e held at 10 degrees C. At 10 degrees C, E. coli O157:H7 was inactivat ed at higher rates in citric, malic, and mandelic acid treatments than in the other treatments. At the pH values tested, the presence of the organic acids enhanced survival of the pathogen at 4 degrees C compar ed with the unacidified control. E. coli O157:H7 has the ability to su rvive in acidic conditions (pH, greater than or equal to 4.0) for up t o 56 days, but survival is affected by type of acidulant and temperatu re.