Occurrence and characterization of plasmid-encoded qnr genes in quinolone-resistant bacteria across diverse aquatic environments in southern Ontario.

Antimicrobial resistance is an ever-increasing threat. The widespread usage of ciprofloxacin has led to the manifestation of resistance due to chromosomal mutations or the acquisition of plasmid-mediated quinolone resistance (PMQR) traits. Some particular PMQR traits, qnr genes, have been identified globally in clinical and environmental isolates. This study aimed to determine the prevalence of ciprofloxacin-resistant bacteria in aquatic environments in southern Ontario and investigate the extent of dissemination of ciprofloxacin resistance traits among the bacterial communities. We surveyed the prevalence of plasmid encoding qnr genes using a multiplex PCR assay of associated PMQR genes, qnrA, qnrB, and qnrS, on 202 isolates. Despite the absence of significant impacts on minimum inhibitory concentration levels, the presence of qnr genes correlates with heightened resistance to quinolones and nalidixic acid in some isolates. Taxonomic analysis highlights distinct differences in the composition and diversity of ciprofloxacin-sensitive (CipS) and ciprofloxacin-resistant (CipR) populations, with Proteobacteria dominating both groups. Importantly, CipR populations exhibit lower genetic diversity but higher prevalence of multiple antibiotic resistances, suggesting co-selection mechanisms. Co-occurrence analysis highlights significant associations between ciprofloxacin resistance and other antibiotic resistances, implicating complex genetic linkages. The results of our study signified the critical role of environmental monitoring in public health.

Widespread detection of antibiotic-resistant bacteria from natural aquatic environments in southern Ontario.

To elucidate how widespread antibiotic resistance is in the surface water environment, we studied the prevalence of antibiotic resistance bacteria at four locations in southern Ontario. We found that the percentage of bacteria resistant to the antibiotic tetracycline was higher at the river site, which flows through agricultural land, and lower at the lake sites. A total of 225 colonies were selected for further testing of antibiotic disc susceptibility to eight different antibiotics to calculate the multiple antibiotic resistance (MAR) score and the antibiotic resistance index for each site. Although the isolates from the lake site outside the city displayed resistance to fewer antibiotics, their MAR scores were not significantly different from that of the lake sites adjacent to urban beaches, showing that MAR was widespread in the natural water environments tested. Isolation of colonies under selection pressure to tetracycline was found to have a significant effect on the likelihood that the isolates would contain multiple resistance traits for other antibiotics. Identification of isolates selected on tetracycline was compared with that of isolates that were sensitive to tetracycline, and the community composition was found to be distinctly different, although isolates from the genera Chryseobacterium, Pseudomonas, and Stenotrophomonas were found in both communities.