Detection of plasmid-mediated quinolone resistance genes in β-lactamase-producing Escherichia coli isolates from layer hens.

This study was conducted to investigate the presence of plasmid-mediated quinolone resistance (PMQR) genes in β-lactamase-producing Escherichia coli isolates from layer hens and to characterize their molecular background. Among 142 E. coli isolates, 86 (60.6%) showed multidrug resistance and 15 (10.6%) were found to be β-lactamase-producing E. coli. Extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC (pAmpC) β-lactamase genes, blaCTX-M-14 and blaCMY-2, were identified in three and six E. coli isolates, respectively. The non-ESBL or pAmpC gene, blaTEM-1, was found in eight of the isolates. Two isolates had both genes, blaCTX-M-14 and blaTEM-1. Among the 15 β-lactamase-producing E. coli, six PMQR genes, qnrS1 (n = 3) and qnrB4 (n = 3), were identified. Among the six PMQR-positive E. coli isolates, four exhibited double amino acid exchanges at both gyrA and parC with ciprofloxacin and enrofloxacin minimum inhibitory concentrations of ≥32 and ≥16 μg/mL, respectively. Additionally, five transconjugants (33.3%) showed a transferability of β-lactamase and PMQR genes. Pulsed-field gel electrophoresis (PFGE) analysis was conducted to investigate the 15 β-lactamase-producing E. coli isolates. In PFGE, E. coli included three PFGE patterns showing the same farms and in accordance with both β-lactamase and PMQR genes and the antimicrobial resistance pattern. Layer hens may act as a reservoir of antibiotic-resistant bacteria, and the PMQR gene in β-lactamase-producing E. coli isolates from layer hens has the potential to enter the food chain. Therefore, our findings suggest that comprehensive surveillance of antimicrobial use in laying operation systems is necessary.