Antibiotic resistance is a global threat of complex and changeable epidemiology. The role of wild birds in the dissemination of antibacterial resistance might be underestimated. We studied the cloacal colonization by cefotaxime-resistant Enterobacteriaceae in 668 wild birds in Spain. Eighty-eight wild birds (13.2%) of 28 species carried cefotaxime-resistant isolates; 58 of them (8.7%) carried extended-spectrum β-lactamases (ESBLs) and 15 (2.5%) plasmid-mediated AmpCs of the bla family. The 58 ESBLs belonged to the CTX-M-1 group (63.9%), CTX-M-9 group (23%), and SHV-group (13.1%). Pulsed field gel electrophoresis (PFGE) analysis of the Escherichia coli isolates revealed a high degree of genetic diversity since 44 different PFGE patterns were observed among the 54 cefotaxime-resistant isolates analyzed. Two clusters were detected with a genetic linkage >90%: Cluster 1 included nine CTX-M-15-producing isolates of ST23, and Cluster 2 included four isolates producing plasmid mediated AmpC of the CIT family of ST744. In addition, five birds were colonized by OXA-48- and CTX-M-15-producing isolates: three Klebsiella pneumoniae (isolated from Eurasian eagle-owl, lesser kestrel, and common buzzard), one E. coli (common buzzard), and one Enterobacter cloacae (cattle egret). Also, an mcr-1-positive and CIT-producing E. coli isolate colonized a black vulture. By multilocus sequence typing, the three OXA-48-producing K. pneumoniae isolates belonged to the high-risk human clones ST11 (two) and ST15 (one); the OXA-48-producing E. coli belonged to ST23, and the mcr-1-positive E. coli belonged to ST162. The diversity of eating patterns and migratory habits of the multiple avian species, capable of carrying multiresistant bacteria as observed in this study, may contribute to their global dissemination from human sources.

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The presence of AMR bacteria in the human–animal–environmental interface is a clear example of the One Health medicine. Several studies evidence the presence of resistant bacteria in wildlife, which can be used as a good indicator of anthropization level on the ecosystem. The fast increase in AMR in the environment in the last decade has been led by several factors as globalization and migration. Migratory birds can travel hundreds of kilometers and disseminate pathogens and AMR through different regions or even continents. The aim of this study was to compare the level of AMR in three migratory bird species: Ciconia ciconia, Larus fuscus and Chroicocephalus ridibundus. For this purpose, commensal Escherichia coli has been considered a useful indicator for AMR studies. After E. coli isolation from individual cloacal swabs, antimicrobial susceptibility tests were performed by the disk-diffusion method, including 17 different antibiotics. A total of 63.2% of gulls had resistant strains, in contrast to 31.6% of white storks. Out of all the resistant strains, 38.9% were considered multi-drug resistant (50% of white storks and 30% of seagulls). The antibiotic classes with the highest rate of AMR were betalactamics, quinolones and tetracyclines, the most commonly used antibiotic in human and veterinary medicine in Spain.

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