Isolation and characterisation of Shiga toxins producing Escherichia coli in dairy cows in the governorate of Blida (Algeria).

Abstract

The Shiga toxin producing Escherichia coli (STEC) are considered to be one of the most important groups of emerging public health pathogens with cattle being the main reservoir. The objective of this study was to isolate and characterise Escherichia coli Shiga toxins in dairy cattle farms. A total of 252 faeces samples were collected from healthy cows belonging to 37 farms. PCR screening of samples for the common sequences of stx1/stx2 genes and stx1 and stx2 genes resulted in a STEC faecal excretion prevalence of 59.5% at the farm level and 26.6% at the individual level. Among positive animals, 85.1% carried STEC with a single stx1 gene and 14.9% with the stx1 and stx2 genes. Immunomagnetic separation was performed on 40 PCR-positive samples (10/10 positive for the stx1 and stx2 genes and 30/57 positive only for stx1). Biochemical identification revealed the presence of 66 E. coli strains (27.5%). The search for virulence genes on these strains by PCR showed that only twenty-two (33.33%) were STEC. The presence of the stx1, stx2, ehx and eae genes was characterised in 30.3%, 4.54%, 13.63% and 1.51% of the strains, respectively, indicating that the virulotype with stx alone was dominant. Serological identification showed the absence of O157 sero-groups and the presence of O1(2), O2, O18(2), O128 sero-groups. The susceptibility testing of STEC showed 68.18% resistance to chloramphenicol, 63.64% to neomycin, 59.1% to ampicillin, 22.73% to trimethoprim + sulfamethoxazole and 9.1% to amoxicillin + clavulanic acid and nalidixic acid. Four strains showed multi-resistance. Bovine carriage of STEC constitutes a public health risk by contamination of milk and meat. To protect human health, it is necessary to limit the bovine STEC shedding.