Whole genome sequencing to characterize shiga toxin-producing Escherichia coli O26 in a public health setting

Background: Shiga-toxin producing Escherichia coli (STEC) O26:H11 is the second most common cause of severe diarrhea and hemolytic uremic syndrome worldwide. The implementation of whole genome sequencing (WGS) enhances the detection and in-depth characterization of these non-0157 STEC strains. The aim of this study was to compare WGS to phenotypic serotyping and pulse field gel electrophoresis (PFGE) for characterization of STECO26 strains following a zoonotic outbreak from cattle to humans. Methods and results: This study evaluated seven E. coli strains; two strains isolated from two children with gastrointestinal symptoms and five strains from five calves suspected as the source of infection. Six of these isolates were serotyped phenotypically and by WGS as E. coli 026:H11 while one bovine isolate could be serotyped only by WGS as E. coli 0182:H25. Stxl was detected in two human- and two bovine-isolates using PCR and WGS. Using WGS, all four STECO26 isolates belong to sequence type (ST) 21 while the two stxl negative E. coli 026 were ST29. All four STECO26 isolates were indistinguishable by PFGE. However, the data generated by WGS linked the two human STECO26 isolates to only one bovine STECO26 strain by having identical high-quality single nucleotide polymorphisms (hqSNPs) and identical virulence factor profiles while the remaining bovine STECO26 isolate differed by 7 hqSNPs and lacked virulence factor toxB. Conclusions: These data demonstrated that WGS provided significant information beyond traditional epidemiological tools allowing for comprehensive characterization of the STEC. Using this approach, WGS was able to identify the specific source of infection in this study. (C) 2019 Published by Elsevier Limited on behalf of King Saud Bin Abdulaziz University for Health Sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons.orgi licensesiby-nc-nd/4,0).