Diversity and antimicrobial resistance of Enterococcus from the Upper Oconee Watershed, Georgia

Aim: It is well-known that enterococci are abundant in the environment; however, the role of surface water as a reservoir of antimicrobial-resistant enterococci remains largely undefined. In this study, surface water samples were collected over a 2-year period from the Upper Oconee watershed, Athens, GA to examine enterococci and their antimicrobial resistance.

Methods and results: Approximately 97% (445/458) of the samples were positive for enterococci and a total of 637 enterococci were isolated. The predominant species were Enterococcus casseliflavus (33·6%) followed by Enterococcus faecalis (26·5%) and Enterococcus hirae (13·2%). Regardless of species, the highest levels of resistance were to lincomycin (88·5%) and tetracycline (13%); isolates also exhibited resistance to newer antimicrobials, daptomycin (8·9%) and tigecycline (6·4%). Multidrug resistance (resistance ≥3 antimicrobial classes) was observed to as many as five classes of antimicrobials. Resistant enterococci appeared to be randomly dispersed over the seasons rather than clustered by species or antimicrobial resistance.

Conclusions: This study demonstrated that surface waters contain a large population of diverse species of antimicrobial-resistant enterococci, including resistance to new antimicrobials.

Significance and impact of the study: These results may indicate the potential of human intestinal illness and/or colonization of the human gut with resistant enterococci as enterococci correlate with increased disease risk to humans during recreational exposure to water.