Purpose: Although present worldwide, this serotype has been majorly described in Europe but little data about O26 molecular epidemiology is available for other continents thus it is unknown if these findings also apply for the United States. We wanted to determine the different populations of O26 E. coli present in US cattle.
Methods: We sequenced 42 O26:H11 strains from US healthy cattle (collected during 3 months in 2011) using MiSeq and compared them to O26:H11 genomes available at NCBI using a wgMLST analysis.
Results: We found as observed in Europe, O26:H11/H- in US cattle are highly diverse, with at least 5 different populations. Most strains were sequence type 29 (ST29). Two clear Lineages could be distinguished among ST29 strains isolated from cattle. Lineage 1 composed of O26:H11 EHEC-like (ST29) and O26:H11 EHEC (ST21), and Lineage 2 showing four diverse populations with different virulence content. Overall our analysis showed US healthy cattle carried pathogenic (ST21, stx1+, ehxA+, toxB+) and also potentially pathogenic (ST29, ehxA+, toxB+) O26:H11 E. coli strains. Furthermore showed that O26:H11 clinical strains from US belonged to a different clone (mostly ST21, stx1+, ehxA+, toxB+) than the newly emerged O26:H11/H- clone in Europe (ST29, stx1+ and/or stx2+, ehxA+, and etpD+).
Significance: Our results showed that whole genome sequence analysis is a robust and valid approach to identify, and genetically characterize E. coli O26:H11, which is of paramount importance for food supply safety and public health.