Wild birds as potential bioindicators of environmental antimicrobial resistance: A preliminary investigation

Antimicrobial resistance (AMR) is an issue of global concern that includes human, animal, and environmental health. To tackle this phenomenon, a One Health approach is required through the involvement of all these interconnected elements. The environment poses challenges for investigation, but wildlife animals, not directly exposed to antibiotic treatments and interacting with their habitats, can serve as indicators of AMR contamination. Specifically, wild birds could play a significant role in dissemination of AMR, as they can acquire AMR bacteria from wildlife reservoirs and disperse them through environments. This study aims to assess the prevalence of AMR in commensal bacteria isolated from wild birds and their role as bioindicators of environmental AMR. A total of 73 birds belonging to various species were sampled in the Emilia-Romagna region with buccal, cloacal and feather samplings. The samples were cultured on selective media, colonies were identified using MALDI-TOF technology and antimicrobial susceptibility to different drugs was assessed using the Kirby-Bauer method. The birds' data were statistically evaluated in relation to AMR percentages. In total, 117 bacterial strains were isolated, belonging to 23 genera and 46 different bacterial species. The highest non-susceptibility percentages were observed for tetracycline (12.2 %) and enrofloxacin (8.6 %) considering all bacterial isolates, as well as for oxacillin (46.8 %), clindamycin (29.3 %) and rifampicin (20.8 %), among Gram-positive isolates. In the statistical analysis, a higher AMR percentage was correlated with Gram-positive isolates from birds belonging to rural/urban habitat (p = 0.01). Among Gram-positives, a higher oxacillin non-susceptibility percentage was found to be associated with isolates from birds sampled in province of Bologna (p = 0.007), a higher enrofloxacin non-susceptibility percentage revealed an association with rural/urban habitat (p = 0.02), while a higher non-susceptibility percentage towards rifampicin resulted associated with isolates from migratory birds (p = 0.031). In conclusion, this preliminary study suggests a potential role of wild birds as bioindicators for monitoring AMR contamination in the environment.