Construction and Validation of Antibiotic Resistance Escherichia coli O157: H7 Strains for Acidic Foods

Abstract

Acid injured bacteria are sensitive to selective agents. Enumeration of such bacteria in selective media therefore results in lower estimation of viable cell counts. In this study, several antibiotic resistant Escherichia coli O157: H7 strains were constructed and their recovery in acidic conditions on several agar media was validated. Introduction of nalidixic acid or rifampicin-resistant strains did not affect either their growth rate or sensitivity against acidic challenge. Recovery of such resistant strains on tryptic-soy agar (TSA) supplemented with corresponding antibiotic was higher than that of other selective media used, and the use of antibiotic-resistant strains or TSA medium supplemented with corresponding antibiotic did not affect the estimation of recovery. These results suggested that the antibiotic resistant strains could be useful for the challenge tests of acidic food.