Commensal and opportunistic bacteria resistant to fourth-generation cephalosporins or fluoroquinolones isolated from yellow-legged gulls (Larus michahellis) settled in Taranto, Southern Italy

Antimicrobial resistance (AMR) is a major global health challenge and its circulation in wildlife is garnering increasing attention. Seabirds, such as the yellow-legged gull (Larus michahellis), which inhabit the interface between marine and anthropogenic environments and exhibit synanthropic habits, are valuable targets for investigating AMR. Therefore, this study focused on the dissemination of bacteria resistant to the critically important antimicrobials (CIA) cefepime (CEP) and enrofloxacin (ENR), by sampling the cloacal content of 15 L. michahellis nestlings. Twenty-seven strains resistant to CEP and/or ENR were isolated. Enterobacter hormaechei subsp. hoffmannii was the most represented species, and all those isolates shared the same multidrug resistance profile. Ten resistant strains belonged to the genus Enterococcus, while three strains belonging to the Bacillus cereus complex were CEP resistant. No horizontal transfer of CEP or ENR resistance was observed. High rates of resistance to trimethoprim/sulphametoxazole, streptomycin, tetracycline, and chloramphenicol were detected. The study evidences the wide presence of CIA-resistant bacteria in L. michahellis, indicating that yellow-legged gulls may contribute to the environmental dissemination of clinically relevant resistances. This highlights the potential bidirectional circulation of resistant bacteria between anthropogenic sources and natural ecosystems, thereby increasing the likelihood of exposure to humans, domestic animals, and wildlife.