Surveillance of Shiga-toxin producing Escherichia coli in Irish sheep

Abstract

Shiga-toxin producing Escherichia coli (STEC) is a foodborne zoonotic pathogen of significant public health concern. Ruminant animals are considered the primary reservoir of STEC. STEC predominantly colonises the lower gastro-intestinal tract, termed the recto-anal junction (RAJ). The number of STEC shed in the faeces of ruminants can vary widely with some animals, termed ‘super-shedders’ (>Log104 c.f.u. g−1 faeces), high risk carriers of the pathogen. The objective of this study was to sample a large cohort of Irish sheep, with quantitative and qualitative analysis of each sample for STEC. RAJ swab samples (N=410) were collected over a 9 month period from an ovine slaughtering facility. Each swab was enriched in 30 ml of modified Tryptone Soya Broth with Novobiocin at 41.5 °C for 5 h and subjected to a quantitative real-time PCR assay to detect and enumerate serogroups O157 and O26 in super-shedding animals. Incubation was allowed to continue for 24 h and shiga-toxin prevalence was assessed using a targeted qualitative real-time PCR assay. Eight O157 strains were isolated, of which six were super-shedding strains. The incidence of stx, O157 and O26 positive swabs was 49.3 %, 1.95 % and 0.24 % respectively. The prevalence of stx1, stx2 and stx1/stx2 virulence factors in isolated strains was 15.9 %, 8.8 % and 22.4 %. Additionally, the occurrence of stx1/stx2 in combination with eaeA in strains was found to be significant according to Pearson’s correlation and a paired T-test. In conclusion, these results underline the risk Irish sheep pose as a potential source of STEC infection.