Purpose: The aims of this study were (i) to screen bovine samples by real-time PCR for Shiga toxin genes and the top-five serogroups, and (ii) to isolate strains from selected PCR-positive samples.
Methods: From 573 slaughtered cattle (aged 3-24 months) fecal samples were collected in seven abattoirs. After enrichment (mTSB with novobiocin), samples were examined by real-time PCR for stx and if positive for the top-five STEC serogroups. From the collective of O26, O145 and O157 PCR-positive samples, strain isolation was attempted by serogroup-specific colony dot-blot hybridization after immunomagnetic separation. Isolated strains were examined for stx1, stx2 and eae (intimin).
Results: Of 563 samples with evaluable results, 74.1% tested positive for stx. Amongst them, serogroups O145, O103, O26, O157 and O111 were detected in 41.9%, 25.9%, 23.9%, 7.8% and 0.8%, respectively. From 95 O26, 166 O145 and 30 O157 PCR-positive samples, 17 O26, 28 O145 and 12 O157 strains were isolated. The 17 O26 strains were eae-positive but only nine strains harbored stx (eight possessing stx1 and one stx2). Of the 28 O145 strains, ten were eae-positive including four harboring stx1 or stx2, whereas 18 were negative for stx and eae. Five of the 12 O157 strains harbored stx2 and eae, did not ferment sorbitol, and were identified as STEC O157:H7/H-. The other seven O157 strains were negative for stx and eae or positive only for eae.
Significance: Shiga toxin genes were frequently found in young Swiss cattle at slaughter and the top-five STEC serogroups, especially O26, O103 and O145, were also detected amongst the stx-positive samples. However, success rates for strain isolation were low and only few of the isolated strains showed a virulence pattern of human pathogenic STEC.