Occurrence of Shiga toxin-producing Escherichia coli carrying antimicrobial resistance genes in sheep on smallholdings in Bangladesh.

Background: Shiga toxin-producing Escherichia coli (STEC) are zoonotic foodborne pathogens and a significant concern with the emergence of antibiotic resistance. Close human contact might have a higher chance of being transmitted to humans from sheep if the sheep population is a potential reservoir of antimicrobial-resistant STEC. Therefore, this study aimed to examine the sheep population in rural Bangladesh for antimicrobial-resistant STEC.

Methods: We screened 200 faecal samples collected from sheep in three Upazilas from the Chattogram district. Randomisation of sampling was not performed due to the smaller flock size (two to six animals per smallholding). Phenotypically positive E. coli isolates were examined for two Shiga toxin-producing genes - stx1 and stx2. PCR-positive STEC isolates were investigated for the presence of antimicrobial resistance (AMR) genes - bla , sul1 and sul2.

Results: In total, 123 of the 200 tested samples were confirmed positive E. coli using culture-based methods. PCR results show 17 (13.8%) E. coli isolates harboured ≥ one virulent gene (stx1 or/and stx2) of STEC. The AMR profile of STEC isolates was determined utilising the disc diffusion method. Of the STEC isolates, 82, 76, 71 and 71% were susceptible to chloramphenicol, gentamicin, ciprofloxacin and ampicillin. In contrast, 47% of isolates were resistant to trimethoprim-sulfamethoxazole, and 41% were resistant to amoxicillin. In addition, six of the tested STEC isolates exhibited the bla  gene; eight STEC isolates had the sul1 gene, and the sul2 gene was detected in ten STEC isolates.

Conclusion: To our knowledge, this study is the first to reveal a substantial percentage of STEC isolated from sheep in rural Bangladesh harbouring AMR genes.