High Prevalence of Plasmid-Mediated Quinolone Resistance in Salmonella enterica Serovars Isolated From Surface Water.

Considering the increasing reports of Salmonella enterica strains resistant to quinolones, antimicrobials frequently employed as therapeutic agents globally, our goal was to investigate the occurrence of plasmid-mediated quinolone resistance (PMQR) determinants in S. enterica recovered from natural surface waters in Paraíba state, Brazil. Water samples (n = 230) were collected monthly in triplicate using modified Moore swabs from 29 sampling sites belonging to 10 large dams. After conventional microbial isolation, representative isolates (n = 938) were submitted to whole genome sequencing, assembly and annotation. Antimicrobial resistance genes (ARGs) were identified, and core genome multilocus sequence typing (cgMLST) was used to infer phylogenetic relationships. Among recovered S. enterica, 130 (13.9%) isolates harboured PMQR determinants; 124 (95.4%) harboured qnrB19, while 6 (4.6%) harboured qnrS1. Multiple other ARGs associated with resistance to aminoglycosides, β-lactams, sulphonamides, tetracyclines and fosfomycin were identified. The diversity of ARGs and plasmids suggests a highly complex resistance landscape. Phylogenetic analysis revealed clustering by serovar and sequence type but not by resistance profile or geographic origin. The absence of association between phylogeny and ARGs highlights the potential role of horizontal gene transfer in disseminating resistance genes in water. Our findings reinforce the importance of antimicrobial resistance surveillance in surface waters.