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

Authors: CHO, SOHYUN - University Of Georgia; Hiott, Lari; MCDONALD, JACOB - University Of Georgia; Barrett, John; MCMILLAN, ELIZABETH - University Of Georgia; House, Sandra; Adams, Eric; Frye, Jonathan; Jackson, Charlene

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2019
Publication Date: 12/13/2019
Citation: Cho, S., Hiott, L.M., Mcdonald, J., Barrett, J.B., Mcmillan, E., House, S.L., Adams, E.S., Frye, J.G., Jackson, C.R. 2019. Diversity and antimicrobial resistance of Enterococcus from the Upper Oconee Watershed, Georgia. Journal of Applied Microbiology. 128(4):1221-1233. https://doi.org/10.1111/jam.14550.
DOI: https://doi.org/10.1111/jam.14550

Interpretive Summary: 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 during each of four seasons from 2015 to 2016 from the Upper Oconee Watershed, located in Athens, GA. Enterococci were isolated, identified to species, and tested for susceptibility against a panel of antimicrobials. At least 10 enterococcal species were detected during the sampling period. The predominant species were Enterococcus casseliflavus followed by E. faecalis and E. hirae. Regardless of species, the highest levels of resistance were to lincomycin and tetracycline; isolates also exhibited resistance to two newer antimicrobials, daptomycin and tigecycline. Multi-drug resistance 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. These results may indicate the potential of human intestinal illness and/or colonization of the human gut with resistant enterococci as enterococci are considered an indicator of water health and correlate with increased disease risk to humans during recreational exposure to water. This information is useful to environmental scientists and state and federal environmental regulatory agencies as they develop policy regarding conservation of water sources.

Technical Abstract: 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 during each of four seasons over a two year period (2015 and 2016) from the Upper Oconee Watershed, located in Athens, GA. Approximately 97% (445/458) of the samples were positive for enterococci; 637 enterococci were isolated, identified to species, and tested for susceptibility against a panel of 16 antimicrobials. At least 10 enterococcal species were detected during the sampling period. The predominant species were Enterococcus casseliflavus (214/637; 33.6%) followed by E. faecalis (169/637; 26.5%) and E. hirae (84/637; 13.2%). Regardless of species, the highest levels of resistance were to lincomycin (88.5%) and tetracycline (13%); isolates also exhibited resistance to two newer antimicrobials, daptomycin (8.9%) and tigecycline (6.4%). Multi-drug resistance (MDR; 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. This study demonstrated that surface waters of the Upper Oconee Watershed contain a large population of diverse species of antimicrobial resistant enterococci, including resistance to new antimicrobials used to treat human infections. These results may indicate the potential of human intestinal illness and/or colonization of the human gut with resistant enterococci as enterococci are considered an indicator of water health and correlate with increased disease risk to humans during recreational exposure to water.