Genomic comparison of Escherichia coli serotype O103:H2 isolates with and without verotoxin genes: implications for risk assessment of strains commonly found in ruminant reservoirs

The E. coli serotype O103:H2 occurs as VTEC carrying only vtx1 or both vtx1 and vtx2, but also as verotoxin negative atypical enteropathogenic E. coli (aEPEC). The majority of human cases of disease are caused by the VTEC form. If aEPEC/VTEC conversions occur, aEPEC strains must be considered a significant public health concern. In the presented study, we have characterized and compared aEPEC and VTEC isolates of O103:H2 from Swedish cattle. 14 isolates of E. coli O103:H2 with and without verotoxin genes were collected from faecal samples taken during a nationwide cattle prevalence study 2011-2012. Isolates were sequenced with a 2x100bp setup producing >100x coverage per isolate. Single nucleotide polymorphism (SNP) typing was performed using GATK. Virulence genes and other regions of interest were detected. Susceptibility to transduction by verotoxin-encoding phages ?731 (?vtx2::cat) and 933W (?vtx2::cat) was investigated for a representative aEPEC O103:H2 isolate.