Analysis of drug resistance mediated by the AcrAB-TolC efflux pump system in avian pathogenic Escherichia coli

Abstract Aims This study investigated the role of the AcrAB-TolC efflux pump in mediating multidrug resistance in avian pathogenic Escherichia coli (APEC) isolated from diseased poultry on large-scale farms in Jilin Province, China, and assessed the ability of efflux pump inhibitors to reverse such resistance. Methods and Results Thirty AcrAB–TolC–positive avian pathogenic Escherichia coli (APEC) strains were isolated from diseased poultry samples. Antimicrobial susceptibility testing was performed using the broth microdilution method in accordance with CLSI guidelines. These isolates exhibited high levels of resistance to six antibiotics, with resistance rates to enrofloxacin and ciprofloxacin reaching 100%. Upon the addition of efflux pump inhibitors—carbonyl cyanide m-chlorophenylhydrazone (CCCP) and BDM91270—the minimum inhibitory concentrations (MICs) of most antibiotics decreased markedly, by up to 64-fold for ceftiofur and 32-fold for gentamicin. RT-qPCR analysis was carried out on a representative multidrug-resistant strain (A25) exhibiting strong efflux activity, which revealed significantly elevated acrB expression consistent with efflux-mediated resistance. Conclusions AcrAB-TolC is widespread and overexpressed in avian E. coli, contributing significantly to multidrug resistance. Inhibitor treatments restored antibiotic susceptibility, indicating that optimized inhibitors represent a promising approach to counter resistance.