Modeling the growth/no growth response of Non-O157 Shiga toxin-producing Escherichia coli to temperature, pH and water activity

Abstract

The objective of this study was to model the effect of temperature, pH and water activity (aw) on the growth/no growth response of non-O157 Shiga toxin-producing E. coli (STEC). A cocktail of six-serogroup STEC was inoculated into brain heart infusion broth (BHI) with 48 combinations of different pH and aw, and the inoculated medium was incubated at one of ten temperatures. After 62 days of incubation, growth was determined by turbidity and plating on tryptic soy agar. Binary data (0 [no growth] or 1 [growth]) were fitted into a nonlinear logistic regression and the parameters were estimated. The model was validated with independently produced data from seven serogroups of non-O157 STEC, a cocktail of E. coli O157:H7, and two panels of six-serogroup of STEC. The non-O157 STEC did not grow at temperatures ≤6 °C and ≥47 °C, and the highest tolerance to pH and aw occurred at 25 °C. Although slight difference in the growth/no growth response was observed among different groups of STEC, the developed model can be applied to all the STECs with an average concordance of 92.3%. This work provides valuable insight into the growth/no-growth response of STEC under various environmental conditions.