Whole-Genome Sequence Reveals Genetic Determinants of the Colonization of Shiga Toxin-Producing Escherichia coli O22:H8 Isolates in Cattle.

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic foodborne pathogen responsible for different cases and outbreaks of severe enteric diseases in humans worldwide. Our group previously showed that Argentine O22:H8 isolates (155 and 182) interfere with the colonization of O157:H7 in an experimental infection bovine model. In this study, we applied a comparative genomic and genome-wide association study (GWAS) analysis to explore the differences between the genetic bases of O22:H8 and O157:H7 strains isolated from cattle. The whole-genome sequence of O22:H8 155 and 182 isolates was compared with 33 O22:H8 and 156 O157:H7 isolates from bovine. Our results showed that O22:H8 isolates harbor genes associated with specific metabolic pathways related to the metabolism of products of vegetal origin, which are absent in O157:H7 isolates. These O22:H8 isolates also carry classical genes of the locus of adhesion and autoaggregation related to the adhesion of non-O157 isolates. In addition, we showed that the T6SS-1 cluster related to bacterial competition predicted in the Argentine O22:H8 isolates is absent both in O157:H7 and other O22:H8 isolates. We also predicted for the first time the locus of type VI secretion system 1 (LT6SS-T1), a genomic island that harbors both T6SS-1 cluster genes and genes related to STEC pathogenesis. This study reveals a subset of genes present in the Argentine O22:H8 isolates that could confer an advantage over O157:H7 during the colonization process in the bovine intestinal tract.