Characteristics of Shigatoxin-Producing Strains Isolated during 2010-2014 from Human Infections in Switzerland.

The aim of this study was to characterize a collection of 95 Shigatoxin-producing .coli (STEC) isolated from human patients in Switzerland during 2010-2014. We performed O and H serotyping and molecular subtyping. The five most common serogroups were O157, O145, O26, O103, and O146. Of the 95 strains, 35 (36.8%) carried genes only, 43 strains (45.2%) carried and 17 (17.9%) harbored combinations of and genes. (42 strains) and (32 strains) were the most frequently detected subtypes. Genes for intimin (), hemolysin (), iron-regulated adhesion (), and the subtilase cytotoxin subtypes , or 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 -ξ, , and 66.7% additionally harboring . 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 -ξ, , and pS88 related genes suggests an ongoing emergence in Switzerland of an unusual, highly pathogenic STEC serotype. 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 variants, and the recently emerged STEC O80:[H2]-ST301 harboring -ξ and pS88 associated extraintestinal pathogenic virulence genes.