Emergence and genetic heterogeneity of STEC O113:H4: insights from whole-genome sequences of isolates across human and non-human sources.

The increased detection of Shiga toxin-producing Escherichia coli (STEC) O113:H4 among human cases in Belgium questions the importance of this serotype as an emerging pathogen. However, detailed information focusing on serotype O113:H4 from human and non-human sources remains limited. We analysed a collection of 140 STEC O113:H4 isolates and their whole genomes, originating from animal hosts (cattle, deer, goats, and sheep), food, and humans, to determine their genetic relationship and assess key virulence genes. All STEC O113:H4 genomes lacked the locus of enterocyte effacement (LEE) and belonged to Pasteur Sequence Type (pST) 367 complex, dominated by pST367 (ehxA-, stx2d+) and pST1729 (ehxA+, stx2b+). Compared to stx2d+ isolates, stx2b+ isolates carried on median more virulence factors, which might thus contribute to enhanced pathogenicity. Besides, humans appear to be infected with distinct subgroups of STEC O113:H4 carrying distinct stx subtypes and originating from potentially different sources: deer, goats, and sheep for STEC carrying stx2b (alone or in combination with stx1c) and mainly cattle for STEC carrying stx2d. Our results call for improved understanding and continuous surveillance of emerging STEC O113:H4.