Antimicrobial resistance gene detection and plasmid typing among multidrug resistant enterococci isolated from freshwater environment

Authors: CHO, SOHYUN - Orise Fellow; Barrett, John; Frye, Jonathan; Jackson, Charlene

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2020
Publication Date: 9/2/2020
Citation: Cho, S., Barrett, J.B., Frye, J.G., Jackson, C.R. 2020. Antimicrobial resistance gene detection and plasmid typing among multidrug resistant enterococci isolated from environmental water. Microorganisms. 8(9):1338. https://doi.org/10.3390/microorganisms8091338.
DOI: https://doi.org/10.3390/microorganisms8091338

Interpretive Summary: Antimicrobial resistant enterococci released into surface water through human and agricultural wastes are a public health concern, not only due to human exposure to these bacteria through water-related activities, but also due to potential dissemination of genes encoding antimicrobial resistance (AR) to other bacteria present in the environment. Previously, we determined prevalence of enterococci that were resistant to antimicrobials commonly used in human and veterinary medicine from surface water of the Upper Oconee Watershed in GA, USA. For the current study, a portion of 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. Resistance mechanisms could not be determined for many of the resistant isolates which indicated that diverse AR mechanisms exist among environmental enterococci, and understanding of AR mechanisms for enterococci is limited. Furthermore, environmental enterococci carried multiple plasmids through which AR genes can be transferred, which 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. This study also indicates that surface water may be a suitable environment for the transfer of AR genes through plasmids harbored by enterococcal isolates present in the aquatic environment.

Technical Abstract: In this study, mechanisms of antimicrobial resistance (AR) as well as abundance and diversity of plasmids were determined among multidrug resistant enterococci from surface water in GA, USA. A total of 51 enterococci isolates were screened for the presence of 26 AR genes conferring resistance to ciprofloxacin, erythromycin, tylosin, kanamycin, streptomycin, lincomycin, Quinuprisitin/Dalfopristin (Q/D), and tetracycline. A plasmid classification system based on replication genes was used to detect 19 defined Gram-positive plasmid replicon families. Eleven 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)], 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 also 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 understanding of AR mechanisms for environmental enterococci is limited. Diverse rep-families were identified among the enterococci recovered from the aquatic environment, which appears 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.