Abstract:

The aim of the present study was to evaluate antimicrobial susceptibilities of enterococci isolated from water, soil, waste, and food samples to determine resistance mechanisms and their transferability, and to test clonality of these environmental enterococci. The results were compared with the susceptibility patterns of hospital enterococci reported in a previous study. Samples from 9 environmental sources were cultured, and species were identified using 16S rRNA sequencing. Antimicrobial susceptibilities were determined by the agar dilution method. The minimum inhibitory concentrations were tested for vancomycin, tetracycline, teicoplanin, ampicillin, gentamicin, erythromycin, rifampicin, clindamycin, chloramphenicol, and ciprofloxacin. Resistance genes and transposons were determined by polymerase chain reaction. The transferability of resistance was tested by conjugation. A total of 57 enterococci were isolated. All erythromycin-resistant enterococci had ermB and all tetracycline-resistant isolates had tetM genes. Macrolide and tetracycline resistances were transferable by conjugation to Enterococcus faecalis JH2-2. Transconjugants were confirmed by pulsed-field gel electrophoresis analysis. Our study showed the existence of antimicrobial resistance among bacteria isolated from environmental samples. All isolates were resistant to at least one antibiotic tested. Transferability of resistance genes in environmental enterococci showed the importance of environmental resistance for public health and the potential of resistance gene dissemination. Although the sample collection times of environmental and hospital isolates were different, the possibility exists that the difference in susceptibility patterns may be the result of differences in antimicrobial pressure in hospitals and in the environment, and this should be studied further.

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