Patterns and persistence of antibiotic resistance in faecal indicator bacteria from freshwater recreational beaches

Aims: This study was conducted to determine antibiotic susceptibility patterns among the faecal indicator bacteria (FIB), Escherichia coli and enterococci, and to determine the potential for freshwater beaches to serve as reservoirs of resistance genes where transfer of resistant phenotypes takes place or de novo resistance may evolve. Methods and Results: One hundred and forty-seven E. coli and 150 enterococci collected from sand and water at recreational beaches along Lake Huron, Michigan, USA were screened against commonly used antibiotics. Resistance was apparent in both E. coli (19% resistant) and enterococci (65% resistant). Antibiotic-resistant E. coli were capable of growing in beach sand microcosms and were able to transfer a plasmid-encoded kanamycin-resistance gene in sand microcosms. Furthermore, resistant phenotypes were stable in the sand environment even in the absence of the corresponding antibiotic. Conclusions: Antibiotic-resistant FIB were prevalent and persistent in the beach habitat. Significance and Impact of the Study: Active populations of FIB at beaches express antibiotic resistance phenotypes and have the ability to transfer antibiotic resistance. These human-associated bacteria may be intermediaries in the movement of resistance between environmental and clinical reservoirs.