Prevalence of sorbitol non-fermenting Shiga toxin-producing Escherichia coli in Black Bengal goats on smallholdings

Abstract

A cross-sectional survey was carried out in Bangladesh with the sampling of 514 Black Bengal goats on smallholdings to determine the presence of sorbitol non-fermenting (SNF) Shiga toxin-producing E. coli (STEC). Swab samples collected from the recto-anal junction were plated onto cefixime and potassium tellurite added sorbitol MacConkey (CT-SMAC) agar, a selective medium for STEC O157 serogroup, where this serogroup and other SNF STEC produce colourless colonies. The SNF E. coli (SNF EC) isolates obtained from the survey were investigated by PCR for the presence of Shiga toxin-producing genes, stx1 and stx2, and two other virulence genes, eae and hlyA that code for adherence factor (intimin protein) and pore-forming cytolysin, respectively. The SNF EC isolates were also assessed for the presence of the rfbO157 gene to verify their identity to O157 serogroup. The results revealed that the proportions of goats carrying SNF EC isolates and stx1 and stx2 genes were 6·2% (32/514) [95% confidence interval (CI) 4·4-8·7)], 1·2% (95% CI 0·5-2·6) and 1·2% (95% CI 0·5-2·6), respectively. All the SNF STEC tested negative for rfbO157, hlyA and eae genes. The risk for transmission of STEC from Black Bengal goats to humans is low.

Keywords: Black Bengal goats; E coli; shiga toxin.

Fig. 1.

Results of PCR assay for four virulent genes: stx1, stx2, hlyA and eae. (a) stx1 gene (614 bp) amplicon: lane M = 1 kb plus DNA ladder; lanes 1, 3–7, stx1-positive isolates; (b) stx2 gene (779 bp) amplicon: lane M = 1 kb plus DNA ladder; lanes 1–7, stx2-positive isolates; (c) hlyA gene (165 bp) amplicon: lane M = 1 kb plus DNA ladder; lanes 4, 9–10, hlyA-positive isolates; (d) eae gene (881 bp) amplicon: lane M = 1 kb plus DNA ladder; lane 2, eae-positive isolate.