Shiga toxin-producing Escherichia coli (STEC) serogroups O26, O45, O103, O111, O121, and O145, referred to as the top six non-O157 serogroups, are responsible for more than 70% of human non-O157 STEC infections in North America. Cattle harbor non-O157 strains in the hindgut and shed them in the feces. The objective of this study was to use the U.S. Food and Drug Administration (FDA) E. coli identification (ECID) DNA microarray to identify the serotype, assess the virulence potential of each, and determine the phylogenetic relationships among five of the six non-O157 E. coli serogroups isolated from feedlot cattle feces. Forty-four strains of STEC, enterohemorrhagic E. coli (EHEC), enteropathogenic E. coli (EPEC), or putative nonpathotype E. coli (NPEC) of cattle origin and five human clinical strains of EHEC were assayed with the FDA-ECID DNA microarray. The cattle strains harbored diverse flagellar genes. The bovine and human strains belonging to serogroups O26, O45, and O103 carried stx1 only, O111 carried both stx1 and stx2, and O145 carried either stx1 or stx2. The strains were also positive for various subtypes of intimin and other adhesins (IrgA homologue adhesin, long polar fimbriae, mannose-specific adhesin, and curli). Both human and cattle strains were positive for LEE-encoded type III secretory system genes and non-LEE-encoded effector genes. SplitsTree4, a program used to determine the phylogenetic relationship among the strains, revealed that the strains within each serogroup clustered according to their pathotype. In addition to genes encoding Shiga toxins, bovine non-O157 E. coli strains possessed other major virulence genes, including those for adhesins, type III secretory system proteins, and plasmid-borne virulence genes, similar to human clinical strains. Because virulence factors encoded by these genes are involved in the pathogenesis of various pathotypes of E. coli, the bovine non-O157 strains could cause human illness. The FDA-ECID DNA microarray assay rapidly provided a profile of the virulence genes for assessment of the virulence potential of each strain.
Keywords: Feces; Feedlot cattle; Genomic characterization; Microarray; Non-O157.