Effect of severe weather events on the shedding of Shigatoxigenic Escherichia coli in slaughter cattle and phenotype of serogroup O157 isolates

High-event periods (HEPs) occur sporadically when beef carcasses and meat have episodes of acute contamination with Shiga toxin-producing Escherichia coli (STEC). In this study, severe weather events were investigated as catalysts for HEPs based on PCR and isolate prevalence of seven E. coli serogroups in slaughter cattle feces. Winter ambient temperatures with daily means 10.5oC warmer or 12.3°C colder than seasonal norms (-10.4°C) most altered STEC shedding. Fecal samples yielded increased proportions (P < 0.05) of O26 and O157 isolates during winter warm periods, and reduced (P < 0.05) O45 isolates during cold periods compared to samplings during seasonal norms. Based on changing PCR prevalence and isolates collected, O157 was the serogroup most responsive to severe weather events. Consequently, O157 isolates (n = 219) were evaluated for heat resistance, biofilm-forming potential and virulence gene subtypes. Two isolates had heat-resistant phenotypes with thermal death time at 60°C (D60) > 10 min and one also had strong biofilm-forming potential. However, this isolate lacked eae and stx genes. Severe weather can influence STEC shedding, particularly of O157, and could possibly trigger HEPs. However, our data suggest that it is unlikely for isolates to carry virulence genes and possess phenotypes capable of evading post-harvest microbiological interventions.