Characterisation of plasmids harbouring extended-spectrum cephalosporin resistance genes in Escherichia coli from French rivers.

Antimicrobial resistance is a "One Health" issue that requires improved knowledge of the presence and abundance of resistant bacteria in the environment. Extended-spectrum cephalosporins (ESCs) are critically important antibiotics (CIAs), and resistance to these CIAs is often encoded by beta-lactamase genes borne on conjugative plasmids. We thus decided to characterise 21 plasmids of ESC-resistant Escherichia coli randomly selected from isolates previously obtained from river water collected in a rural area in western France. The plasmids encoding ESC resistance were sequenced to investigate the diversity of the genes encoding ESC resistance and their genetic context. Sequences revealed that eleven IncI1 pMLST3 plasmids carried the blaCTX-M-1 and sul2 genes, and some of them also had the tet(A), aadA5 or dfrA17 genes. The blaCTX-M-1 gene was also detected on an IncN plasmid. Five plasmids obtained from four rivers contained blaCTX-M-14, either on IncI1 or on IncFII plasmids. Two strains from two rivers contained blaCTX-M-15 on IncN pMLST7 plasmids, with qnrS1 and dfrA14 genes. One plasmid contained the blaCTX-M-55, a blaTEM-1B-like, and fosA genes. One plasmid contained the blaCMY-2 gene. The diversity of the genes and plasmids of the resistant bacteria isolated from French rivers is probably related to the various animal and human origins of the isolated bacteria.