Comparison of whole genome sequences from human and non-human Escherichia coli O26 strains

Authors: NORMAN, KERI - Former ARS Employee; Clawson, Michael - Mike; STROCKBINE, NANCY - Centers For Disease Control And Prevention (CDC) - United States; Mandrell, Robert; JOHNSON, ROGER - Public Health Agency Of Canada; ZIEBELL, KIM - Public Health Agency Of Canada; ZHAO, SHAOHUA - Food And Drug Administration(FDA); Fratamico, Pina; STONES, ROBERT - Food And Environmental Research Agency; ALLARD, MARC - Food And Drug Administration(FDA); Bono, James - Jim

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2015
Publication Date: 3/11/2015
Publication URL: https://handle.nal.usda.gov/10113/61115
Citation: Norman, K.N., Clawson, M.L., Strockbine, N.N., Mandrell, R.E., Johnson, R., Ziebell, K., Zhao, S., Fratamico, P.M., Stones, R., Allard, M., Bono, J.L. 2015. Comparison of whole genome sequences from human and non-human Escherichia coli O26 strains. Frontiers in Cellular and Infection Microbiology. 5(21). DOI: 10.3389/fcimb.2015.00021.

Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) O26 is the second leading STEC serogroup responsible for human illness outbreaks behind E. coli O157:H7. Recent outbreaks have been linked to emerging pathogenic O26:H11 E. coli strains harboring only the gene for shiga toxin 2 (stx2), not shiga toxin 1 (stx1). Cattle have been recognized as a reservoir of E. coli O26 strains harboring stx1; however, the reservoir of these emerging E. coli O26 strains with only stx2 is unknown. The objective of this study was to identify genetic variation in human- and cattle-derived E. coli O26 strains in order to compare differences in genotypes and virulence gene profiles between the two mammalian hosts. Whole genome sequencing and analyses identified seven genetic clusters within the E. coli O26 strains. The seven clusters did not distinguish between isolates originating from humans or cattle; however, clusters did correspond with particular virulence gene profiles. Results indicate similar genetic strains of E. coli O26 with similar virulent gene profiles were found in cattle and humans. Thus, cattle may serve as a reservoir of the emerging pathogenic E. coli O26:H11 strains harboring stx2 responsible for recent outbreaks.

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) O26 is the second leading E. coli serogroup responsible for human illness outbreaks behind E. coli O157:H7. Recent outbreaks have been linked to emerging pathogenic O26:H11 strains harboring stx2 only. Cattle have been recognized as an important reservoir of O26 strains harboring stx1; however the reservoir of these emerging stx2 strains is unknown. The objective of this study was to identify nucleotide polymorphisms in human and cattle-derived strains in order to compare differences in polymorphism derived genotypes and virulence gene profiles between the two host species. Whole genome sequencing was performed on 182 epidemiologically unrelated O26 strains, including 111 human-derived strains and 71 non-human-derived strains (59 of cattle origin). A panel of 289 O26 strains (241 STEC and 48 non-STEC) was subsequently genotyped using a set of 283 polymorphisms identified by whole genome sequencing, resulting in 64 unique genotypes. Phylogenetic analyses identified seven clusters within the O26 strains. The seven clusters did not distinguish between isolates originating from humans or cattle; however, clusters did correspond with particular virulence gene profiles. Human and non-human-derived strains harboring stx1 clustered separately from strains harboring stx2, strains harboring eae, and non-STEC strains. Strains harboring stx2 were more closely related to non-STEC strains and strains harboring eae than to strains harboring stx1. The finding of human and cattle-derived strains with the same polymorphism derived genotypes and similar virulence gene profiles, provides evidence that similar strains are found in cattle and humans and transmission between the two species may occur. Cattle may serve as an important reservoir of the emerging pathogenic O26:H11 strains harboring stx2, responsible for recent outbreaks.