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), lactic (pH 4.7), malic (pH 4.0), mandelic (pH 5.0), or tartaric (pH 4.1) acid 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 days was determined. Triplicate flasks were prepared for each acid treatment at each temperature. At 25 degrees C, populations increased 2 to 4 log(10) CFU/ml in all treatments except that with mandelic acid, whereas no growth occurred at 10 or 4 degrees C in any treatments except the control. However, at all sampling times, higher (P < 0.05) populations were recovered from treatments held at 4 degrees C than from those held at 10 degrees C. At 10 degrees C, E. coli O157:H7 was inactivated 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 compared with the unacidified control. E. coli O157:H7 has the ability to survive in acidic conditions (pH, greater than or equal to 4.0) for up to 56 days, but survival is affected by type of acidulant and temperature.