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 109 human-derived strains and 73 non-human-derived strains. 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.
Highlights
Shiga toxin-producing Escherichia coli (STEC) O26:H11/NM has emerged as an important human pathogen capable of causing severe cases of diarrhea and hemolytic uremic syndrome (HUS) (Misselwitz et al, 2003)
Sequencing Coverage of O26 Strains A total of 1.233 GB of sequence was produced in the study, with 591 MB originating from the pool of 111 human strains, and 642 MB originating from the pool of 71 non-human strains
We identified 283 nucleotide polymorphisms in conserved regions of the chromosome that were utilized for MALDITOF genotyping of 180 sequenced strains and an additional 109 O26 E. coli strains
Summary
Shiga toxin-producing Escherichia coli (STEC) O26:H11/NM has emerged as an important human pathogen capable of causing severe cases of diarrhea and hemolytic uremic syndrome (HUS) (Misselwitz et al, 2003). Outbreaks of STEC infection have been traced to the O26 serogroup in the United States (Brown et al, 2012), Europe (Werber et al, 2002; Ethelberg et al, 2009; Buvens et al, 2011), and Japan (Misselwitz et al, 2003; Sonoda et al, 2008; Tomita, 2008). Several of the more recent O26:H11 outbreaks include one in a Colorado childcare center in 2011 (Brown et al, 2012), a 2007 ice cream implicated outbreak in Belgium (De Schrijver et al, 2008), and a 2007 outbreak in Denmark traced to beef sausage (Ethelberg et al, 2007). More recently in 2012, 29 individuals from 11 states were infected with an O26 STEC strain traced back to clover sprouts (Centers for Disease Control and Prevention, 2012)
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