Effect of acid adaptation on survival of Escherichia coli O157 : H7 in meat decontamination washing fluids and potential effects of organic acid interventions on the microbial ecology of the meat plant environment

The acid tolerance of Escherichia coli O157:H7 may be pH inducible. Correspondingly, organic acid meat decontamination washing fluids may enhance the establishment of acid-adapted E. coli O157:H7 strains in packing plants, especially in mixtures with water washings from meat that may be of sublethal pH. Acid-adapted and nonadapted cultures of a rifampin-resistant derivative of the acid-resistant E. coli O157:H7 strain ATCC 43895 were tested to evaluate their survival in meat-washing fluids over a wide pH range, The cultures were exposed (10(5) CFU/ml) to acidic (2% lactic acid, 2% acetic acid, or a mixture of the two with water washings at ratios of 1/1, 1/9, or 1/99 [vol/vol]) or nonacid (water) meat washings for up to 14 days at 4 or 10degreesC storage. E. coli O157:H7 survived in water washings, but the low storage temperatures and predominant natural microbiota synergistically inhibited its growth. Compared with acid-adapted populations, nonadapted populations displayed greater potential for survival and a tendency to initiate growth in water meat washings at 10degreesC. The pathogen survived in most of the acid washings throughout storage (14 days), sometimes with minimal population reductions. Overall, nonadapted populations declined faster than acid-adapted populations, while the declines increased as the acid concentration and temperature of storage increased and were more dramatic in lactate, compared to acetate, washings. Acid-containing washings were selective for growth of lactic acid bacteria and yeasts, indicating that organic acid treatments may alter the microbial ecology of meat plant environments and potentially that of the meat. These results should be considered when selecting decontamination technologies for meat.