Influence of acid tolerance responses on survival, growth, and thermal cross-protection of Escherichia coli O157 : H7 in acidified media and fruit juices

A study was done to determine survival and growth characteristics of acid-a dapted, acid-shocked, and control cells of Escherichia coli O157:H7 inocula ted into tryptic soy broth (TSB) acidified with organic acids and three com mercial brands of apple cider and orange juice. The three types of cells be haved similarly in TSB acidified with acetic acid; however, in TSB (pH 3.9) acidified with lactic acid, acid-adapted cells were more tolerant than aci d-shocked cells which, in turn, were more tolerant than control cells. The ability of the three types of cells to grow after inoculation into acidifie d TSB, then plated on tryptic soy agar containing sodium chloride was deter mined. Tolerance of acid-adapted cells and, less markedly, acid-shocked cel ls to sodium chloride was diminished, compared to control cells. The pathog en showed extraordinary tolerance to the low pH of apple cider and orange j uice held at 5 or 25 degrees C for up to 42 days. Growth occurred in one br and of apple cider (pH 3.98) incubated at 25 degrees C. Regardless of test parameters, there was no indication that cell types differed in tolerance t o the acidic environment in apple cider or orange juice. Survival of contro l, acid-adapted, and acid-shocked cells heated in apple cider and orange ju ice was studied. Within each apple cider or orange juice, D-52 degrees C-va lues of acid-adapted cells were considerably higher than those of acid-shoc ked or control cells, which indicates that heat tolerance can be substantia lly enhanced by acid adaptation compared to acid shock. (C) 1998 Elsevier S cience B.V. All rights reserved.