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

Thomas Douellou (1, 2) , S. Delannoy (3) , S. Ganet (1) , P. Fach (1) , Estelle Loukiadis (1) , Marie-Christine Montel (2) , Delphine Thevenot-Sergentet (1)

1 LEM - Laboratoire d'Ecologie Microbienne - UMR 5557
2 UMRF - Unité Mixte de Recherche sur le Fromage
3 LSAl - Laboratoire de sécurité des aliments de Maisons-Alfort

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 0157, 026 and 0103 STEC strains isolated from raw-milk dairy products by analyzing virulence-related gene frequencies and associations with O-island (OI) 44, 01-48, 01-50, 01-57, 01-71 and 01-122. Results showed that 100% of STEC strains investigated harbored genes associated with EHEC-related virulence profile patterns (eae and stx, with either espK, espy, 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:rni SP 026E but not genetic markers espK, espy, 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.

Mots clés: O157 STEC; dairy products; virulence genetic markers; non-O157 STEC; dairy product

Mots clés: marqueur génétique; escherichia coli; shiga toxine; produit laitier

Domaines: Microbiologie et Parasitologie

Thomas Douellou, S. Delannoy, S. Ganet, P. Fach, Estelle Loukiadis, et al.. Molecular characterization of O157:H7, O26:H11 and O103:H2 shiga toxin-producing escherichia coli isolated from dairy products. International Journal of Food Microbiology, 2017, 253, pp.59-65. ⟨10.1016/j.ijfoodmicro.2017.04.010⟩. ⟨hal-01607979⟩