Selective concentration for ciprofloxacin resistance in Escherichia coli grown in complex aquatic bacterial biofilms

There is concern that antibiotics in the environment can select for and enrich bacteria carrying acquired antibiotic resistance genes, thus increasing the potential of those genes to emerge in a clinical context. A critical question for understanding and managing such risks is what levels of antibiotics are needed to select for resistance in complex bacterial communities. We address this question by examining the phenotypic and genotypic profiles of aquatic communities exposed to ciprofloxacin, also evaluating the within-species selection of resistant E. coli in complex communities. These findings can be used to define and implement discharge or surface water limits to reduce risks for selection of antibiotic resistance in the environment.