Antibiotic resistance assessment in bacteria isolated in migratory Passeriformes transiting through the Metaponto territory (Basilicata, Italy)

Background: Wild birds are considered to be reservoirs of human enteric pathogens and vectors of antimicrobial resistance dissemination in the environment. During their annual migration, they play a potential role in the epidemiology of human associated zoonoses. The aim of this study was to investigate the frequency of isolation and antimicrobial susceptibility profiles of microorganisms found in the cloaca of common European passerines. Methods: One hundred and twenty-one cloacal swabs were collected during a monitoring program of migratory birds in the Forest Reserve for Protection "Metaponto" (Basilicata, Italy). All samples were cultured using standard bacteriological methods and antibiotic susceptibility testing (agar disk diffusion test) of isolated strains was performed. Results: The bacteriological analysis produced 122 strains belonging to 18 different species. The most commonly isolated species were Enterobacter cloacae and Providencia rettgeri (21 strains, 17.2%). Potentially pathogenic species including Klebsiella pneumoniae, Serratia marcescens and Pseudomonas spp. have also been identified. Isolates showed significant frequencies of antimicrobial resistance. The highest frequency of resistance was observed against amoxicillin (n = 79, 64.8%); ampicillin (n = 77, 63.1%); rifampicin (n = 75, 61.5%); amoxicillin-clavulanic acid (n = 66, 54.1%). Thirty-one strains (25.4%) showed resistance to imipenem and 8 (6.6%) to meropenem. Conclusions: Migratory birds play an important role in the ecology, circulation and dissemination of potentially pathogenic antimicrobial resistant organisms. They can therefore be considered sentinel species and environmental health indicators. Our results suggest that the integration of epidemiological surveillance networks during ringing campaigns of wild species can be an effective tool to study this phenomenon.