Prevalence of some genetic factors determining antimicrobial resistance in commensal Escherichia coli isolated from broilers and laying hens.

Abstract

The aim of the current study was to determine the prevalence of resistance to some antimicrobial agents in commensal Escherichia coli from poultry in Bulgaria. It was performed from June to December 2020 and included 175 strains, 99 of which were isolated from broilers and 76 from laying hens. ESBL phenotypes of isolates were tested for the presence of blaCTX-M-1. The distribution of genes qnrS, qnrA and qnrB1 conferring resistance to quinolones was studied. Also, the resistance to tetracycline and the presence of tetA gene were investigated. A high percentage of resistance towards tetracycline and ciprofloxacin was observed in commensal E. coli isolates from broilers (65.6%, 70.7%, respectively), and a high percentage of resistance to ciprofloxacin (75.0%) in isolates from laying hens. Also, high resistance towards β-lactams ampicillin and amoxicillin/clavulanic acid was observed in isolates from broilers (54.5%, 45.4%), vs 50.0% to ampicillin and 39.5% to amoxicillin/clavulanic acid in isolates from laying hens. Fewer strains resistant to cefotaxime and ceftazidime (8.1 %, 7.1%) were found out in isolates from broilers. None of commensal E. coli strains from laying hens were resistant to cefotaxime and ceftazidime. Five of the cephalosporin-resistant E. coli from broilers (5.0%) were identified as producers of ESBL, possessing the gene blaCTX-M-1. Sixty-five strains from broilers (65.6%) and 50 strains from laying hens (65.8%) possessed the qnrS gene. The qnrA and qnrB1 genes were not detected in ciprofloxacin-resistant E. coli isolates. Sixty-five strains from broilers (65.6%) and 33 strains from laying hens (33.0%) possessed the gene tetA. The commonest profile of multidrug resistance in E. coli isolates from broilers (37.4%) included ampicillin, amoxicillin/clavulanic acid, tetracycline and ciprofloxacin while in isolates from laying hens, resistance to ampicillin, amoxicillin/clavulanic acid and ciprofloxacin predominated (33.0%).