Serotypes and virulence genes of ovine non-O157 Shiga toxin-producing Escherichia coli in Switzerland C. Zweifel a , J.E. Blanco b , M. Blanco b , J. Blanco b , R. Stephan a, * a Institute for Food Safety and Hygiene, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 270, 8057 Zurich, Switzerland b Laboratorio de Referencia de E. coli (LREC), Departamento de Microbioloxı ´a e Parasitoloxı ´a, Facultade de Veterinaria, Universidade de Santiago de Compostela (USC), Lugo, Spain Received 22 December 2003; accepted 18 January 2004 Abstract Sixty ovine STEC strains were examined with the aim (i) to serotype the strains, (ii) to characterize virulence factors, and (iii) to discuss possible associations between these factors and to assess the potential pathogenicity of these strains for humans. The 60 sorbitol-positive, non-O157 STEC strains belonged to 19 O:H serotypes, whereas 68% were of five serotypes (O87:H16, O91:H-, O103:H2, O128:H2, O176:H4). 52% belonged to serotypes reported in association with HUS. Five serotypes were not previously reported in sheep strains. Of the 47 strains encoding for stx1 variants, 57% were stx1c- and of the 45 encoding for stx2 variants, 80% were stx2d-positive. Eighty-two percent of the strains showed further putative virulence factors: 13% were eae-, 60% ehxA- and 67% saa-positive. The associations between harboring (i) eae and stx1, stx2, ehxA or no saa and (ii) saa and stx1c or stx2d were significant ( P < 0.05). The strains belonged to 27 seropathotypes (association between serotypes and virulence factors), but 57% belonged to only six and O91:H-stx1 stx2d saa and O128:H2 stx1c stx2d ehxA saa were the most common. Seven of the eight intimin-positive strains harbored eae q. Four strains of serotype O103:H2 and O121:H10 harboring stx2, eae and ehxA showed virulence factors typical for strains associated with severe human disease. However, according to the virulence factors, the majority of the ovine non-O157 STEC strains are assumed low-virulence variants. Nevertheless, as long as the contribution and interaction of these factors in milder disease remains unclear P, a certain risk for humans cannot be excluded. D 2004 Elsevier B.V. All rights reserved. Keywords: Ovine non-O157 Shiga toxin-producing E. coli (STEC); Serotypes; Shiga toxin types; Virulence factors 1. Introduction Shiga toxin-producing Escherichia coli (STEC) has emerged as a pathogen that can cause food-borne infections and severe and potentially fatal illness in humans. STEC are a cause of human gastroenteritis that may be complicated by hemorrhagic colitis (HC) or hemolytic-uremic syndrome (HUS). STEC strains causing human infections belong to a large, still increasing number of O:H serotypes. A re- view of the world literature on non-O157 STEC isola- tion by K.A. Bettelheim is available on the Micro- BioNet website (http://www.sciencenet.com.au). Most outbreaks and sporadic cases of HC and HUS have been attributed to O157:H7 STEC strains (Blanco et al., 2001; Chapman et al., 2001). However, especially in 0168-1605/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2004.01.015 * Corresponding author. Tel.: +41-635-8657; fax: +41-635- 8908. E-mail address: stephanr@fsafety.unizh.ch (R. Stephan). www.elsevier.com/locate/ijfoodmicro International Journal of Food Microbiology 95 (2004) 19 – 27