Objectives: Wild birds are vectors of antimicrobial resistance. Birds living in close contact with humans or other animals, like feral pigeons (Columba livia), might be especially prone to acquire resistance genes such as those encoding extended-spectrum beta-lactamases (ESBLs) and carbapenemases.
Methods: Cloacal samples (n = 206) of free-living feral pigeons (C. livia) were collected in Sousse and Monastir, Tunisia. Antimicrobial susceptibility profiles were determined by disc-diffusion, and resistant isolates were short- and long-read whole-genome sequenced. Sequence analysis was performed using tools of the Centre for Genomic Epidemiology, and Phylogenetic analysis was performed based on the core-genome MLST.
Results: Fourteen (14/206, 6.8%) pigeons harboured Enterobacterales resistant to last-generations cephalosporins, of which 10 were CTX-M-15- or CTX-M-27-producers, while two (1.0%) carried a VIM-2-producing Pseudomonas putida. Positive pigeons lived on four different livestock farms. Three STs (ST206, ST5584, ST8149) were identified among E. coli, of which ST5584 and ST8149 were found in two different farms. Genetic diversity was also observed in Enterobacter cloacae and P. putida isolates. The blaCTX-M-27 genes were chromosomally encoded, while the blaCTX-M-15 genes were carried on highly similar IncF/F-:A-:B53 plasmids. The blaVIM-2 gene was located on a class 1 integron co-harbouring several resistance genes.
Conclusion: Pigeons living on livestock farms carried clinically important resistance genes encoding ESBLs and carbapenemases. Our results evidenced that both clonal (ST8149 and ST5584) and plasmidic (IncF/F-:A-:B53) transfers played a role in the spread of resistance genes among pigeons. Further studies are needed to identify factors favouring the transfer and persistence of resistance genes within the pigeon communities.
Keywords: ESBL; F-:A-:B53; Horizontal gene transfer; Pigeons; Plasmid; VIM-2.
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