Molecular Characterization of Human Atypical Sorbitol-Fermenting Enteropathogenic Escherichia coli O157 Reveals High Diversity

Abstract

Alongside the well-characterized enterohemorrhagic Escherichia coli (EHEC) O157:H7, serogroup O157 comprises sorbitolfermenting typical and atypical enteropathogenic E. coli (EPEC/aEPEC) strains that carry the intimin-encoding gene eae but not Shiga toxin-encoding genes (stx). Since little is known about these pathogens, we characterized 30 clinical isolates from patients with hemolytic uremic syndrome (HUS) or uncomplicated diarrhea with respect to their flagellin gene (fliC) type and multilocus sequence type (MLST). Moreover, we applied whole-genome sequencing (WGS) to determine the phylogenetic relationship with other eae-positive EHEC serotypes and the composition of the rfbO157 region. fliC typing resulted in five fliC types (H7, H16, H34, H39, and H45). Isolates of each fliC type shared a unique ST. In comparison to the 42 HUS-associated E. coli (HUSEC) strains, only the stx-negative isolates with fliCH7 shared their ST with EHEC O157:H7/H ؊ strains. With the exception of one O157:H ؊ fliCH16 isolate, HUS was exclusively associated with fliCH7. WGS corroborated the separation of the fliCH7 isolates, which were closely related to the EHEC O157:H7/H ؊ isolates, and the diverse group of isolates exhibiting different fliC types, indicating independent evolution of the different serotypes. This was also supported by the heterogeneity within the rfbO157 region that exhibited extensive recombinations. The genotypic subtypes and distribution of clinical symptoms suggested that the stx-negative O157 strains with fliCH7 were originally EHEC strains that lost stx. The remaining isolates form a distinct and diverse group of atypical EPEC isolates that do not possess the full spectrum of virulence genes, underlining the importance of identifying the H antigen for clinical risk assessment.

Characteristics of Shigatoxin-Producing Escherichia coli Strains Isolated during 2010–2014 from Human Infections in Switzerland

“…The five most common serogroups in this study belonged to a limited number of CC and ST, whereas the vast majority of the remaining STEC strains were represented by a total of 28 STs, 24 of which contained only a single isolate. CC11 comprised all the O157 STEC, including the SF strains, confirming high clonality of this serogroup as described previously (Bielaszewska et al, 2007 ; Kossow et al, 2016 ). Furthermore, this CC included an isolate belonging to O55, which is in accordance to its evolutionary relatedness to O157 (Bono et al, 2012 ).…”

Sorbitol-Fermenting Enterohemorrhagic Escherichia coli O157:H − Isolates from Czech Patients with Novel Plasmid Composition Not Previously Seen in German Isolates

“…Similar strains, i.e., stx-negative SF E. coli O157:H Ϫ (fliC H7 ) harboring sfpA but lacking EHEC-hlyA, were recently reported for patients with HUS or diarrhea in Germany (50). These strains clustered with SF EHEC O157:H Ϫ in the WGS-based analysis (50), corroborating their descent from SF EHEC O157:H Ϫ by stx 2a loss (50). Altogether, these findings indicate that a subset of SF EHEC O157:H Ϫ strains of the novel Czech clone may occur as stx-negative variants.…”

“…Since SF EHEC O157:H Ϫ strains can frequently lose their stx 2a genes via loss of stx 2a -harboring phages (38,49), these strains plausibly represent stx-negative variants of the novel SF EHEC O157:H Ϫ clone. Similar strains, i.e., stx-negative SF E. coli O157:H Ϫ (fliC H7 ) harboring sfpA but lacking EHEC-hlyA, were recently reported for patients with HUS or diarrhea in Germany (50). These strains clustered with SF EHEC O157:H Ϫ in the WGS-based analysis (50), corroborating their descent from SF EHEC O157:H Ϫ by stx 2a loss (50).…”

Severe Outbreak of Sorbitol‐Fermenting Escherichia coli O157 via Unpasteurized Milk and Farm Visits, Finland 2012

“…As suggested by Kossow et al. (), stx ‐negative SF O157 strains harbouring the gene encoding for H7 antigen ( fliC H7 ) possibly represent STEC that lost their stx . The presence of fliC H7 was confirmed in the Egyptian, Mexican and Turkish studies.…”