The Heat Resistance of Escherichia Coli Cells From Cultures of Different Ages

SUMMARY: From the mortality curves of Escherichia coli cells heated at 55° in Ringer's solution both Decimal Reduction Times (DRTs) and 99–9% mortality times were obtained. In terms of these measures of heat resistance, cells harvested from broth cultures 0–8 hr old were more susceptible than those from more mature cultures. The time of commencement and the approximate duration of the logarithmic phase of growth of the organism in broth were determined from growth curves, and it was observed that the heat resistance was minimal during that phase. Death rates were not always uniform for the whole of a given population. Particularly among young cultures, a period of rapid death was frequently followed by the slower death of a relatively small number of survivors. In one instance only was an initial period of slow death followed by one of more rapid death.