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Diversity of Shiga toxin-producing Escherichia coli (STEC) O26:H11: characterization of stx subtypes and insertion sites of Stx and EspK bacteriophages

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Bonanno, L. | Loukiadis, Estelle | Mariani-Kurkdjian, P. | Oswald, E. | Garnier, L. | Michel, V. | Auvray, F.

Edité par CCSD ; American Society for Microbiology -

International audience. Shiga toxin-producing Escherichia coli (STEC) are food-borne pathogens that may be responsible for severe human infections. Only a limited number of serotypes, including O26:H11, are involved in the majority of serious cases and outbreaks. The main virulence factors, Shiga-toxins (Stx), are encoded by bacteriophages. Seventy four STEC O26:H11 strains of various origins (including human, dairy and cattle) were characterized for their stx subtypes and Stx phage chromosomal insertion sites. The majority of food and cattle strains possessed the stx1a subtype, while human strains mainly carried either stx1a or stx2a. The wrbA and yehV genes were the main Stx phage insertion sites in STEC O26:H11, followed distantly by yecE and sbcB. Interestingly, the occurrence of Stx phages inserted into the yecE gene was low in dairy strains. In most of 29 stx-negative E. coli O26:H11 strains also studied here, these bacterial insertion sites were vacant. Multilocus sequence typing of 20 stx-positive or stx-negative E. coli O26:H11 showed that they were distributed into two phylogenetic groups defined by sequence type (ST) 21 and ST29. Finally, an EspK-carrying phage was found inserted into the ssrA gene in the majority of STEC O26:H11 but only in a minority of stx-negative E. coli O26:H11. The differences of stx subtypes and Stx phage insertion sites observed in STEC O26:H11 according to their origin might reflect that strains circulating in cattle and foods are clonally distinct from those isolated from human patients.

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