Acid resistance of enterohaemorrhagic and generic Escherichia coli associated with foodborne disease and meat

Abstract

As part of the Australia New Zealand Food Authorities (ANZFA) food standards code, salami manufacturers are required to demonstrate that their process is capable of achieving a 3-log reduction in Escherichia coli. Non-pathogenic E. coli strains with similar or greater acid resistance to enterohaemorrhagic E. coli (EHEC) are needed if industry is to conduct challenge studies to demonstrate compliance with the standard. In the present study, E. coli isolates from sheep and beef carcasses and meat were shown to have wide-ranging acid resistance in broth when preadapted to growth in acidic conditions. Times required for a 3-log reduction in E. coli ranged from less than 1 day to more than 28 days. Variable acid resistance was observed in both EHEC strains associated with foodborne outbreaks and generic E. coli strains. Generic E. coli strains with the greatest acid resistance were assessed for pathogenicity markers and their survival in fermented meat compared with EHEC strains. It was demonstrated that generic E. coli strains could be used for challenge studies to determine compliance with or validate performance standards designed for the control of EHEC.