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

Abstract

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.

Antimicrobial Resistance Gene Detection and Plasmid Typing Among Multidrug Resistant Enterococci Isolated from Freshwater Environment

“…In our previous study, most of the Enterococcus isolates from surface water were resistant to at least one antimicrobial drug with multiple resistant phenotypes identified in a total of 51 isolates [12]. For the current study, those isolates that were resistant to three or more antimicrobial classes were further tested to investigate the molecular mechanism of AR and the abundance and diversity of plasmids among enterococci from surface water.…”

“…pEF1071 is a member of rep 11 family, and enterocins 1071A and 1071B are known to be encoded on pEF1071 [45]. Since enterocins exhibit antimicrobial activity and the producer bearing the plasmid would have a survival advantage over other closely related species present in the same ecological niche [45], it is possible that the presence of pEF1071 enabled E. casseliflavus to be the most frequently identified species and also the most common species with MDR phenotypes found in the surface water [12].…”

“…Enterococci were isolated from surface water of the Upper Oconee Watershed, GA, USA, and their AR patterns were described in our previous study [12]. From the previous study, a total of 637 enterococci were isolated, of which, 93.1% (593/637) were resistant to at least one of the 16 antimicrobial drugs tested [12]. A total of 51 multidrug resistant (MDR; resistance ≥ 3 antimicrobial classes) Enterococcus isolates were used in the present study.…”

“…The significance of enterococci as clinically important pathogens is often associated with acquisition of AR via horizontal gene transfer using mobile genetic elements, especially plasmids in the strains. In our previous study, we demonstrated prevalence of enterococci that are resistant to antimicrobials commonly used in human and veterinary medicine from surface water of the Upper Oconee Watershed in GA, USA [12]. To further characterize AR in enterococci from freshwater environments, mechanisms conferring AR were examined.…”

Escherichia coli Antimicrobial Resistance Variability in Water Runoff and Soil from a Remnant Native Prairie, an Improved Pasture, and a Cultivated Agricultural Watershed

“…In recent years, research has gained momentum on the topic of studying AMR and MDR in nonclinical and opportunistic environmental bacteria [5][6][7][8][9][10]. Some of these more recent studies on environmental resistance have revealed the prevalence of AMR and MDR in bacteria in soil [11][12][13], water bodies and watersheds [14][15][16][17][18][19][20][21][22][23][24], oceans [25]; glaciers [26], and animals [27,28]. For example, D'Costa et al [11] found MDR in all 480 soil isolates they screened for the 21 major classes of antibiotics.…”