Population changes and verotoxin production of enterohemorrhagic Escherichia coli strains inoculated in milk and ground beef held at low temperatures

This study investigated the influence of low temperature and background flora on growth and verotoxin production by strains of enterohemorrhagic Escherichia coli in milk and ground beef. In the presence of no or low background flora, there was growth of the strains at 8 degrees 0. High background flora in ground beef inhibited growth at this temperature. In the foods held at low temperatures, only small amounts of verotoxin were detected; however, even at the optimum 37 degrees C, there was still relatively little verotoxin formed compared to that in broth cultures. Even under nongrowth conditions (high background flora or 5 degrees C holding temperature), the strains remained viable. These data suggest any food contaminated by these bacteria and held at the recommended temperature of 5 degrees C will remain hazardous, and under certain conditions, holding at temperatures greater than or equal to 8 degrees C would increase the hazard.