Growth and survival of various strains of enterohemorrhagic Escherichia coli in hydrochloric and acetic acid

Nineteen strains of enterohemorrhagic Escherichia coli isolated from humans and foods were examined for their ability to grow and survive at low pH in organic (acetic) and mineral (HCl) acids. Strains were subcultured in tryp tic soy broth adjusted to various pH values (3.75 to 4.75 for HCl and 4.75 to 5.75 for acetic acid) and incubated for 72 h at 37 degrees C to determin e the minimum growth pH value. Minimum pH values for growth of 4.25 and 5.5 were found for HCl and acetic acid, respectively. Strains were also expose d to pH 2.0 (HCl) and pH 4.0 (acetic acid) for up to 24 h at 37 degrees C t o assess their ability to survive. HCl was a more effective inhibitor after 6 h of exposure, whereas acetic acid was more effective after 24 h. Outbre ak strains survived acid treatment significantly (P less than or equal to 0 .05) better than strains isolated from fermented or high-pH foods or animal or human isolates. Significant (P less than or equal to 0.05) differences among serotypes and between O157:H7 and other serotypes were apparent after 3 or 6 h of exposure to acids.