Surface waters are important sources of water for drinking, industrial, agricultural, and recreational uses; hence, contamination of water by fecal, pathogenic, or antimicrobial resistant (AR) bacteria is a major environmental and public health concern. However, very little data is available on prevalence of these bacteria in surface water throughout a watershed. This study aimed to characterize Escherichia coli present in the Upper Oconee Watershed, a mixed-use watershed in Athens, GA, USA for potential pathogenicity and AR. E. coli were enumerated by colony counts, cultured by enrichment and direct plating, and characterized by phylo-groups, diarrheagenic pathotypes, and antimicrobial susceptibility. From the analysis, 99.3% (455/458) of the total samples were positive for E. coli resulting in 496 isolates. E. coli counts were as high as 1.2×104 CFU/100 ml, which is above the United States Environmental Protection Agency (U.S. EPA) threshold for recreational water (235 CFU/100 ml based on a one-time measurement). Phylo-groups B2 (31.7%; 157/496) and B1 (30.8%; 153/496) were the most prevalent among the isolates. Enteropathogenic E. coli (EPEC) (19/496) and Shiga toxin-producing E. coli (STEC) (1/496) were the only diarrheagenic pathotypes detected. AR was observed in 6.9% (34/496) of the isolates, 15 of which were multidrug resistant (MDR; resistance to two or more classes of antimicrobials). Tetracycline resistance was most often detected (76.5%; 26/34), followed by ampicillin (32.4%; 11/34), streptomycin (23.5%; 8/34), sulfisoxazole (23.5%; 8/34), and nalidixic acid (14.7%; 5/34). Results from this study showed that E. coli is prevalent in high levels in the Upper Oconee Watershed, suggesting possible widespread fecal contamination. The presence of pathogenic, AR E. coli in the watershed indicates that environmental water can serve as a reservoir of resistant bacteria that may be transferred to humans through drinking and recreational activities.
In this study, mechanisms of antimicrobial resistance (AR) as well as the abundance and diversity of plasmids were determined among multidrug resistant (MDR) enterococci from surface water in GA, USA. A total of 51 enterococci isolates were screened for the presence of 27 AR genes conferring resistance to ciprofloxacin, erythromycin, tylosin, kanamycin, streptomycin, lincomycin, Quinupristin/Dalfopristin (Q/D), and tetracycline. A plasmid classification system based on replication genes was used to detect 19 defined Gram-positive plasmid replicon families. Twelve genes were identified as conferring resistance to erythromycin and tylosin (erm(B) and erm(C)), kanamycin (aph(3′)-IIIa), streptomycin (ant(6)-Ia), lincomycin (lnu(B)), Q/D (vat(E)), ciprofloxacin (qnrE. faecalis), and tetracycline (tet(K), tet(L), tet(M), tet(O) and tet(S)). Twelve different rep-families were identified in two-thirds of the isolates. While AR genes commonly found in human and animals were detected in this study among environmental enterococci, resistance genes could not be determined for many of the isolates, which indicates that diverse AR mechanisms exist among enterococci, and the understanding of AR mechanisms for environmental enterococci is limited. Diverse rep-families were identified among the enterococci recovered from the aquatic environment, and these rep-families appear to be quite different from those recovered from other sources. This work expands knowledge of AR gene reservoirs and enterococcal plasmids across a wider range of environments.
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.
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