Influence of acidulant identity on the effects of pH and acid resistance on the radiation resistance of Escherichia coli O157:H7

The effects of pH (4.0–5.5), acid identity (acetic, citric, lactic, malic, and hydrochloric), and the induction of pH-dependent stationary phase acid resistance on the radiation resistance of E. coli O157:H7 Ent-C9490 was studied using cells grown in Tryptic Soy Broth with and without dextrose (induced and non-induced to acid resistance) and then resuspended in brain–heart infusion broth containing 5 g/l of an organic acid and acidified with concentrated hydrochloric acid. After treatment with gamma radiation, the number of survivors was determined by plating on brain–heart infusion agar (injured and non-injured cells) and MacConkey agar (non-injured cells), and the data used to calculate radiation D-values. The induction of pH-dependent stationary phase acid resistance consistently provided the enterohemorrhagic E. coli strain cross-protection from subsequent irradiation, increasing radiation D-values by 1.2–3.3-fold, depending on the organic acid present. The radiation resistance of E. coli varied with acid identity, but was largely unaffected by pH within the range examined. The results indicate that induction of cross-protection resulting from induction of acid resistance is a factor that should be considered to accurately determine the radiation dose needed to inactivate enterohemorrhagic E. coli in foods. r 2003 Elsevier Ltd. All rights reserved.