Acid resistance and acid adaptation responses of foodborne Escherichia coli isolates

Abstract

Escherichia coli possesses four phenotypically distinct systems of acid resistance (AR). AR is an important characteristic of E. coli, enabling the organism to survive acidic environments. In this study, a wild-type E. coli strain, K12, and two foodborne E. coli isolates were tested for AR. AR systems 2, 3, and 4 required the presence of glutamate, arginine, or lysine, respectively, during acid challenge tests at pH 2.0 after adaptation to HCl or organic acids (pH 5.0). AR characteristics of the two foodborne E. coli isolates were found to be similar to those of the wild-type strain. Nonetheless, survival rates of E. coli strains adapted to lactic acid were higher than those of E. coli strains adapted to HCl or citric acid. Therefore, our results indicate that E. coli strains that survive in foods containing lactic acid as a preservative may have stronger AR for survival under acidic conditions. Practical applicationsEscherichia coli has acid resistance (AR) systems and can mount acid adaptation responses for survival in acidic environments when exposed to even a moderately acidic environment. Organic acidslactic and citric acidsare commonly used in the food industry. In previous studies, however, the prevalence of AR genes in foodborne E. coli isolates has never been determined, and AR of foodborne E. coli isolates and their AR responses after adaptation to organic acids have not yet been investigated. Therefore, in this study, the prevalence of AR genes in foodborne E. coli isolates was evaluated, and their AR after adaptation to lactic and citric acids was determined.