| Summary: | 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 (<i>erm</i>(B) and <i>erm</i>(C)), kanamycin (<i>aph</i>(3′)-IIIa), streptomycin (<i>ant</i>(6)-Ia), lincomycin (<i>lnu</i>(B)), Q/D (<i>vat</i>(E)), ciprofloxacin (<i>qnr<sub>E. faecalis</sub></i>), and tetracycline (<i>tet</i>(K), <i>tet</i>(L), <i>tet</i>(M), <i>tet</i>(O) and <i>tet</i>(S)). Twelve different <i>rep</i>-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 <i>rep</i>-families were identified among the enterococci recovered from the aquatic environment, and these <i>rep</i>-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.
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