Minimum and maximum temperatures for growth and verotoxin production by hemorrhagic strains of Escherichia coli

The influence of temperature on growth and verotoxin production by Escherichia coli strains was studied in brain heart infusion (BHI) broth both in shake cultures at various temperatures and in a temperature-gradient incubator. All strains of E. coli surveyed grew from at least 10 to 45 degrees C, with some strains growing at 8 degrees C. Verotoxin production (determined using the Vero cell-assay system) was a function of both temperature and time, with the highest titers produced at temperatures supporting the fastest growth (based on days to visible turbidity) and highest viable cell counts. However, for strains producing verotoxin, toxin production was detected at any temperature supporting growth. Three strains (of 16 tested) increased 1000-fold in viable count in 4 to 6 days at 10 degrees C. The data presented here indicate that most E. coli strains surveyed can easily grow at ca. 10 degrees C and thus suggest the potential for growth in temperature-abused refrigerated foods