Escherichia coli O157:H7: distribution, molecular characterization, antimicrobial resistance patterns and source of contamination of sheep and goat carcasses at an export abattoir, Mojdo, Ethiopia

Abstract

Background: Cattle have been identified as a major reservoir of E. coli O157:H7 for human infection; the ecology of the organism in sheep and goats is less understood. This study was carried out to determine prevalence, source of infection, antibiotic resistance and molecular characterization of Escherichia coli O157: H7 isolated from sheep and goat.

Methods: Systematic random sampling was carried out at Modjo export abattoir, Ethiopia, from November 2012 to April 2013 to collect 408 samples from 72 sheep and 32 goats. Samples collected were skin swabs, fecal samples, intestinal mucosal swabs and the inside and outside part of carcasses as well as carcass in contacts such as workers hands, knife, hook and carcass washing water. Then, samples were processed following standard bacteriological procedures. Non-Sorbitol fermenting colonies were tested on latex agglutination test and the positives are subjected to PCR for detection of attaching and effacing genes (eaeA) and shiga toxin producing genes (stx1 and stx2). All E. coli O157:H7 isolates were checked for their susceptibility pattern towards 15 selected antibiotics.

Results: E. coli O157:H7 were detected in only 20/408 samples (4.9%). Among these 20 positive samples, 70% (14/20), 25% (5/20) and 5% (1/20) were from sheep, goats and knife samples, respectively. No significant associations were found between carcasses and the assumed sources of contaminations. Of all the 20 isolates virulence genes were found in 10 (50%) of them; 3 (15%) with only the eaeA gene and 7(35%) expressing eaeA and stx2 genes. All the isolates were susceptible to Norfloxacin (NOR) (100%).

Conclusions: The presence of virulence genes shows E. coli O157:H7 is a potential source of human infection in Ethiopia.

Keywords: Abattoir; Antibiotic sensitivity; CT-SMAC; E. coli O157:H7; IMS; Latex agglutination; Multiplex PCR.

Fig. 1

Catchment areas for sheep and goats slaughtered at the abattoir

Fig. 2

Procedures followed during sample collection and processing: a skin swab sample collection; b intestinal mucosal swab sample collection; c fecal sample collection; d carcass outside swab sample collection; e carcass inside swab sample collection; f concentration of E. coli O157:H7 using IMS technique; g antimicrobial susceptibility test bacterial isolates

Fig. 3

Amplification products of eaeA and stx2 virulent genes of E. coli O157:H7 isolated from sheep & goat . M = 100 bp DNA marker; 1–10 PCR products, the amplicon sizes of eaeA and stx2 are 384 bp and 266 bp, respectively; 11 = Negative contro, (PCR grade water)