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 (ARB) 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 antibiotic disc susceptibility testing to 8 different antibiotics to calculate the multiple antibiotic resistance (MAR) and the antibiotic resistance index (ARI) 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 the lake sites adjacent to urban beaches showing that multiple antibiotic resistance 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 were compared with 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.