Short communication: Behavior of different Shiga toxin-producing Escherichia coli serotypes (O26:H11, O103:H2, O145:H28, O157:H7) during the manufacture, ripening, and storage of a white mold cheese.

Ruminants are healthy carriers of Shiga toxin-producing Escherichia coli (STEC). If good hygienic and agricultural practices at the farm level, especially during the milking process, are not adequately followed, milk and dairy products made with raw milk could become contaminated. Sporadic cases and rare food outbreaks have been linked with dairy products. Consequently, understanding STEC behavior in cheeses would help to evaluate risks for human health. The behavior of 4 different STEC strains belonging to the serotypes O26:H11, O103:H2, O145:H28, and O157:H7 were monitored during the manufacture, ripening, and storage of a white mold soft cheese. These strains, originating from dairy products, were inoculated individually in raw milk from cow at 10(2) cfu/mL. During the first 24 to 36h of the manufacturing stage, the STEC level increased by 2 to 3 log10 cfu/g. Over the course of the ripening stage, the concentration of the non-O157 STEC remained relatively constant, whereas a decrease of the E. coli O157:H7 concentration was observed. During the storage stage, the level of the different non-O157 STEC strains decreased slowly in the core and in the rind of cheeses. The non-O157 STEC level reached between 3.1 and 4.1 log10 cfu/g at d 56. Interestingly, the concentration of the E. coli O157:H7 strain decreased dramatically: the strains remained detectable only after enrichment. During ripening and storage, STEC levels were generally higher in rinds than in cheese cores. In contrast to what was seen in cheese cores, the E. coli O157:H7 strain remained enumerable in rinds during these steps. These results highlight that STEC can grow during the manufacture and survive during the ripening and storage of a white mold soft cheese.

Molecular characterization of O157:H7, O26:H11 and O103:H2 Shiga toxin-producing Escherichia coli isolated from dairy products.

Pathogenic Shiga toxin-producing E. coli (STEC) are recognized worldwide as environment and foodborne pathogens which can be transmitted by ingestion of ready-to-eat food such as raw milk-derived products. STEC show a prevalence rate in dairy products of 0.9%, yet comparably few outbreaks have been related to dairy products consumption. In this study, we used rt-qPCR to identify the virulence potential of O157, O26 and O103 STEC strains isolated from raw-milk dairy products by analyzing virulence-related gene frequencies and associations with O-island (OI) 44, OI-48, OI-50, OI-57, OI-71 and OI-122. Results showed that 100% of STEC strains investigated harbored genes associated with EHEC-related virulence profile patterns (eae and stx, with either espK, espV, ureD and/or Z2098). We also found similarities in virulence-related gene content between O157:H7 and O103:H2 dairy and non-dairy STEC strains, especially isolates from human cases. The O26:H11-serotype STEC strains investigated harbor the arcA-allele 2 gene associated with specific genetic markers. These profiles are associated with high-virulence seropathotype-A STEC. However, the low frequency of stx2 gene associated with absence of other virulence genes in dairy isolates of O26:H11 remains a promising avenue of investigation to estimate their real pathogenicity. All O26:H11 attaching-effacing E. coli (AEEC) strains carried CRISPRO26:H11SP_O26_E but not genetic markers espK, espV, ureD and/or Z2098 associated with the emerging potentially high-virulence "new French clone". These strains are potentially as "EHEC-like" strains because they may acquire (or have lost) stx gene. In this study, O157:H7, O103:H2 and O26:H11 STEC strains isolated from dairy products were assigned as potential pathogens. However, research now needs to investigate the impact of dairy product environment and dairy processing on the expression of their pathogenicity.