Abstract
Objectives: The aim of this study was to characterize a collection of 95 Shigatoxin-producing E.coli (STEC) isolated from human patients in Switzerland during 2010–2014.Methods: We performed O and H serotyping and molecular subtyping.Results: The five most common serogroups were O157, O145, O26, O103, and O146. Of the 95 strains, 35 (36.8%) carried stx1 genes only, 43 strains (45.2%) carried stx2 and 17 (17.9%) harbored combinations of stx1 and stx2 genes. Stx1a (42 strains) and stx2a (32 strains) were the most frequently detected stx subtypes. Genes for intimin (eae), hemolysin (hly), iron-regulated adhesion (iha), and the subtilase cytotoxin subtypes subAB1, subAB2-1, subAB2-2, or subAB2-3 were detected in 70.5, 83.2, 74.7, and 20% of the strains, respectively. Multilocus sequence typing assigned the majority (58.9%) of the isolates to five different clonal complexes (CC), 11, 32, 29, 20, and 165, respectively. CC11 included all O157:[H7] and O55:[H7] isolates. CC32 comprised O145:[H28] isolates, and O145:[H25] belonged to sequence type (ST) 342. CC29 contained isolates of the O26:[H11], O111:[H8] and O118:[Hnt] serogroups, and CC20 encompassed isolates of O51:H49/[Hnt] and O103:[H2]. CC165 included isolates typed O80:[H2]-ST301, all harboring stx2d, eae-ξ, hly, and 66.7% additionally harboring iha. All O80:[H2]-ST301 strains harbored at least 7 genes carried by pS88, a plasmid associated with extraintestinal virulence. Compared to data from Switzerland from the years 2000–2009, an increase of the proportion of non-O157 STEC infections was observed as well as an increase of infections due to STEC O146. By contrast, the prevalence of the highly virulent German clone STEC O26:[H11]-ST29 decreased from 11.3% during 2000–2009 to 1.1% for the time span 2010–2014. The detection of O80:[H2]-ST301 harboring stx2d, eae-ξ, hly, iha, and pS88 related genes suggests an ongoing emergence in Switzerland of an unusual, highly pathogenic STEC serotype.Conclusions: Serotyping and molecular subtyping of clinical STEC demonstrate that although STEC O157 predominates among STEC isolated from diseased humans, non-O157 STEC infections are increasing in Switzerland, including those due to STEC O146:[H2/H21/H28]-ST442/ST738 harboring subAB variants, and the recently emerged STEC O80:[H2]-ST301 harboring eae-ξ and pS88 associated extraintestinal pathogenic virulence genes.
Highlights
Shiga toxin (Stx)-producing Escherichia coli (STEC) are important foodborne pathogens and responsible for outbreaks and sporadic cases of gastrointestinal illnesses which may include nonbloody or bloody diarrhea, hemorrhagic colitis (HC), and the hemolytic uremic syndrome (HUS) (Karch et al, 2005)
Non-O157 Shigatoxin-producing Escherichia coli (STEC) serogroups, in particular, O26, O103, O111, and O145, are recognized for their pathogenic potential and constitute together with O157 the so called “top five” serogroups of human pathogenic STEC in the EU (Beutin, 2006; Johnson et al, 2006; EFSA, 2016). Beside this group of five, other STEC serogroups, such as O91 and O121 have been associated with human illness in Germany and Switzerland, respectively (Mellmann et al, 2009; Käppeli et al, 2011a), and O45 and O121 are among the top seven serogroups detected in the U.S.A. (Gould et al, 2013)
This study describes the serotypes, virulence genes and multilocus sequence types of STEC associated with human disease in Switzerland during 2010 and 2014
Summary
Shiga toxin (Stx)-producing Escherichia coli (STEC) are important foodborne pathogens and responsible for outbreaks and sporadic cases of gastrointestinal illnesses which may include nonbloody or bloody diarrhea, hemorrhagic colitis (HC), and the hemolytic uremic syndrome (HUS) (Karch et al, 2005). Non-O157 STEC serogroups, in particular, O26, O103, O111, and O145, are recognized for their pathogenic potential and constitute together with O157 the so called “top five” serogroups of human pathogenic STEC in the EU (Beutin, 2006; Johnson et al, 2006; EFSA, 2016) Beside this group of five, other STEC serogroups, such as O91 and O121 have been associated with human illness in Germany and Switzerland, respectively (Mellmann et al, 2009; Käppeli et al, 2011a), and O45 and O121 are among the top seven serogroups detected in the U.S.A. Identification of such strains is important as it may predict epidemiological changes or indicate novel sources of infection
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