Abstract
Antimicrobial resistance (AMR) is a profound global health challenge bridging human medicine, livestock production, and wildlife ecology. In agricultural landscapes, wild birds frequently forage within livestock-rearing facilities and effluent disposal zones, potentially acquiring and disseminating resistant bacteria. This study investigated the phenotypic and genotypic antimicrobial resistance profiles of Escherichia coli isolates recovered from wild birds inhabiting intensive agricultural matrices across southeastern Australia. A total of 542 fecal and cloacal samples were collected across four avian functional feeding guilds: waterfowl, synanthropic generalists (corvids/artamids), terrestrial herbivores (psittacines), and insectivores. Overall, 312 confirmed E. coli isolates were obtained (recovery rate: 57.6%). Phenotypic antimicrobial susceptibility testing against 14 clinically and veterinary important antimicrobials revealed overall resistance to ampicillin (28.2%), tetracycline (24.0%), and trimethoprim-sulfamethoxazole (18.6%), with 21.8% of isolates demonstrating multidrug resistance (MDR). Multidrug resistance was significantly higher in synanthropic generalists (34.8%) and waterfowl (28.1%) compared to strictly herbivorous psittacines (8.7%). PCR screening detected high frequencies of beta-lactamase genes (blaTEM, blaCTX-M), tetracycline resistance determinants (tetA, tetB), sulfonamide resistance genes (sul1, sul2), and class 1 integrons (intI1). Proximity to intensive cattle feedlots and effluent lagoons was a significant predictor of MDR carriage. These findings demonstrate that free-ranging wild birds act as sensitive environmental bioindicators and potential mobile vectors for the dissemination of antimicrobial resistance determinants across southeastern Australian agro-ecosystems, underscoring the urgent need for integrated One Health surveillance.
