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 backgroun d flora on growth and verotoxin production by strains of enterohemorrh agic Escherichia coli in milk and ground beef. In the presence of no o r low background flora, there was growth of the strains at 8 degrees 0 . High background flora in ground beef inhibited growth at this temper ature. In the foods held at low temperatures, only small amounts of ve rotoxin were detected; however, even at the optimum 37 degrees C, ther e was still relatively little verotoxin formed compared to that in bro th 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 r ecommended 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.