Molecular typing of Escherichia coli O157 isolates from Romanian human cases.

Verocytotoxin-producing Escherichia coli (VTEC) of serogroup O157 are among the most important causes of severe cases of foodborne disease and outbreaks worldwide. As little is known about the characteristic of these strains in Romania, we aimed to provide reference information on the virulence gene content, phylogenetic background, and genetic diversity of seven autochthonous O157 strains collected during 2016 and 2017 from epidemiologically non-related cases. These strains were typed by a combination of phenotypic and molecular methods routinely used by the national reference laboratory. Additionally, four of them were also subjected to whole-genome sequencing (WGS) and public web-based tools were used to extract information on virulence gene profiles, multilocus sequence types (MLST), and SNP-based phylogenetic relatedness. Molecular typing provided evidence of the circulation of a polyclonal population while distinguishing a cluster of non-sorbitol-fermenting, glucuronidase-negative, phylogenetic group E, MLST 1804 strains, representing lineage II and clade 7, which harbored vtx2c, eae-gamma, and ehxA genes. A good correlation between the routine typing methods and WGS data was observed. Yet SNP-based genotyping provided a higher resolution in depicting the relationships between the O157:H7 strains than that provided by PFGE. This study should be a catalyst for improved laboratory-based surveillance of autochthonous VTEC.