Heat resistance of Shiga toxin-producing Escherichia coli and potential surrogates in wheat flour at two moisture levels

Twenty-two Shiga toxin-producing Escherichia coli (STEC) strains and six potential surrogates (E. coli strains K12 and P1, Listeria innocua, Lactobacillus plantarum, Bifidobacterium lactis, and Enterococcus faecium) were screened in wheat flour at two water content levels of 8 and 13% (0.25 and 0.55 water activities) for survival at 6 °C and resistance to a heat treatment at 82 °C for 5 min. The results showed that the moisture content of the flour had a significant impact on the inactivation. The STEC populations were inactivated by an average of 1.7 log CFU/g and 6.0 log CFU/g at 8 and 13% moisture levels, respectively. The STEC strains linked to notorious outbreaks showed viable counts above the average STEC viable counts after storage and after the heat treatment at respective moisture levels. These strains have been incriminated in outbreaks related to food products such as hazelnuts, sprouts, “Jack in the Box” fast food, apple juice, mettwurst sausage and cookie dough. The survival after storage and heat inactivation of E. faecium NRRL-B2354 and E. coli P1 indicated the potential suitability of these bacteria as surrogates for STEC for wheat flour process validations.