Highly Virulent Non-O157 Enterohemorrhagic Escherichia coli (EHEC) Serotypes Reflect Similar Phylogenetic Lineages, Providing New Insights into the Evolution of EHEC

Abstract

Enterohemorrhagic Escherichia coli (EHEC) is the causative agent of bloody diarrhea and extraintestinal sequelae in humans, most importantly hemolytic-uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Besides the bacteriophage-encoded Shiga toxin gene (stx), EHEC harbors the locus of enterocyte effacement (LEE), which confers the ability to cause attaching and effacing lesions. Currently, the vast majority of EHEC infections are caused by strains belonging to five O serogroups (the “big five”), which, in addition to O157, the most important, comprise O26, O103, O111, and O145. We hypothesize that these four non-O157 EHEC serotypes differ in their phylogenies. To test this hypothesis, we used multilocus sequence typing (MLST) to analyze a large collection of 250 isolates of these four O serogroups, which were isolated from diseased as well as healthy humans and cattle between 1952 and 2009. The majority of the EHEC isolates of O serogroups O26 and O111 clustered into one sequence type complex, STC29. Isolates of O103 clustered mainly in STC20, and most isolates of O145 were found within STC32. In addition to these EHEC strains, STC29 also included stx-negative E. coli strains, termed atypical enteropathogenic E. coli (aEPEC), yet another intestinal pathogenic E. coli group. The finding that aEPEC and EHEC isolates of non-O157 O serogroups share the same phylogeny suggests an ongoing microevolutionary scenario in which the phage-encoded Shiga toxin gene stx is transferred between aEPEC and EHEC. As a consequence, aEPEC strains of STC29 can be regarded as post- or pre-EHEC isolates. Therefore, STC29 incorporates phylogenetic information useful for unraveling the evolution of EHEC.

The Accessory Genome of Shiga Toxin-Producing Escherichia coli Defines a Persistent Colonization Type in Cattle

“…Even though only four cattle herds were sampled, albeit intensively, we detected 4 (O26, O103, O145, O157) of the 5 (additionally O111) EHEC O antigens, which define strains that account for most of the human HUS cases in Germany (31,62,63). Three of these were recognized as STEC spo .…”

“…The severe O104:H4 outbreak in Germany in 2011 dramatically underscored the flexibility and adaptability of the STEC pathovar as it was caused by a newly evolved hybrid strain combining virulence properties of both EHEC and enteroaggregative E. coli (EAEC) (30). Recently, Eichhorn and colleagues showed that some atypical enteropathogenic E. coli (aEPEC) and EHEC isolates share the same phylogeny and termed the aEPEC isolates post-or pre-EHEC (31). Horizontal gene transfer constantly lets new STEC and EHEC strains with unforeseeable risk potential for humans arise.…”

Shiga‐toxin Producing Escherichia coli: Pathogenicity, Supershedding, Diagnostic Methods, Occurrence, and Foodborne Outbreaks

“…Infections were related to the consumption by animals of contaminated raw fenugreek (Frank and others ). New pathogenic strains of STEC are always possible, since many of the serotypes evolved from enteropathogenic E. coli (EPEC) (Eichhorn and others ). Phylogenetic studies indicate that a common ancestor may exist for strains of the same H flagellum type, such as O26:H11 and O111:H11, in addition to other STEC strains which may have shared an ancestor common to EPEC strains, such as O111:H2 and O128:H2, O63:H6 and O113:H6 and O55:H6 (Ju and others ; Ferdous and others ).…”

Escherichia coli O157:H7 in Iran: Time to Look Closer

“…11 In addition, the polyphyletic evolutionary events occurred within each serogroup caused more complexity resulting O157 E. coli belonging to different clonal complexes (CC). [12][13][14] Recent advances in genomic analysis and use of wider genomic typing approaches like single nucleotide polymorphism (SNP) analysis revealed at least 9 clades in O157: H7 E. coli. 1 Comprehensive studies revealed that only a subset of O157 E. coli exhibit high virulence that is mostly seen in clades 8 and 6.…”

“…17,18 The shared sequence types (ST) between STEC and enteropathogenic E. coli (EPEC) strongly suggest some stx-negative O157 strains to be the progenitors of STEC (pre-STEC) or strains that lost Shiga toxin genes (STEC-LST). 13,17,18 International Journal of Enteric Pathogens Volume 4, Issue 3, August 2016 2…”