Modeling the growth and survival of Shiga toxin-producing Escherichia coli (STEC) in beef

The role of non-O157 STEC in food safety is gaining public concern. The objectives of this study were to: (i) compare the growth of non-O157 STEC with E. coli O157:H7 in a microbiological medium and ground beef, and evaluate the performance of available models (ComBase Predictor, Huang et al. model, and Cepeda et al. model) for the prediction of STEC growth in ground beef; (ii) model the effect of temperature, pH and water activity (aw) on the growth/no growth response of non-O157 STEC; and (iii) determine the minimum growth temperature of STEC. The growth data of E. coli O157:H7, O104:H4, O26, O45, O103, O111, O121, O145, and mixtures of non-O157 STEC in modified tryptic soy broth (TSB; pH 5.7) and ground beef (27% or 7% fat) were obtained at time-varying sinusoidal temperature profiles (low [5-15 °C] or high [10-40 °C]). The growth of non-O157 STEC was similar (p \u3e 0.05) to the growth of E. coli O157:H7. Fat content did not affect (p \u3e 0.05) STEC growth in ground beef. Both Combase and Huang et al. model under-estimated the growth of all STEC for both temperature profiles, whereas Cepeda et al. model is considered as a conservative model to predict the STEC growth in ground beef. A growth/no growth boundary model for non-O157 STEC was developed in a culture broth at pH (4.5-7), aw (0.950-0.993), and temperature (6-47 °C). The model was validated with independently produced data using ten groups of STEC. Although slight difference on growth/no growth response existed among different groups of STEC, the developed model can be applied to all the STEC with an average concordance of 92.3%. The minimum growth temperatures of 48 strains of STEC were determined in TSB. The temperatures varied among strains, but the difference was within 2-3 °C. All of the STEC strains grew at ≥10.3 °C, and none of them were able to growth at ≤7.4 °C. In all, this study provides critical information on STEC growth and survival, which could be used either in fundamental research or in risk assessment to estimate the potential risk of STEC in beef products