The effect of incubation temperature, initial pH, and sodium chloride on the growth kinetics of Escherichia coli O157:H7

Abstract

The 6 effects of initial pH, sodium chloride content, and incubation temperature on the aerobic and anaerobic growth kinetics of a three strain mixture of Escherichia coli O157:H7 were evaluated using brain heart infusion broth. The three variables interacted to affect growth, with the primary effects being noted in relation to generation times (GTs) and lag phase durations (LPDs). The maximum population densities (MPDs) achieved by the cultures were largely independent of the three variables; however, there was a general depression of MPDs by 0·5–1·0 log cycles when the cultures were incubated anaerobically. Under otherwise optimal conditions, GTs and LPDs were largely unaffected by initial pH at values ⩾ 5·5. Initial pH had a greater effect when the NaCl content was elevated. Increasing NaCl levels decreased the growth rate of the organism, with the effect being greater if the other variables were also non-optimal. In general, the effect of temperature could be adequately described by the Ratkowsky square root function; however, there was a general depression of optimal growth temperatures and an increase in the differential between Tmin and actual temperature that did not support growth as other variables became non-optimal. Comparison of the current data with previous reports suggest that the growth kinetics of E. coli O157:H7 are similar to those for non-pathogenic strains.