The study of high level gentamicin resistanance in Enterococcus species isolated from healthy human in Tehran, 2007-8

Enterococci are natural inhabitants of the gastrointestinal tract of humans and animals. Over the past decade, enterococci have become one of the leading causes of nosocomial infections,because they have acquired resistance to many antimicrobial agents such as vancomycin and gentamicin.Development of high-level gentamicin resistance among enterococci represents a serious therapeutic problem as it precludes synergy between aminoglycosides and cell-wall active agents. High-level gentamicin resistance (MIC ≥ 500 mg/ml) in enterococci is predominantly mediated by aac (6')-Ie-aph (2'')-Ia gene.. The aim of present study was determination of high level gentamicin resistance in Enterococcus species isolated fromhealthy human in Tehran. After enrichment of the fecal samples collected from healthy volunteers in BHI broth containing gentamicin, the isolates were subcultured on m-Enterococcus agar containing gentamicin. The isolates were identified to the genus and species levels and MIC was determined. Antibiotic susceptibility of the isolates was tested by agar diffusion method for 8 various antibiotics. The aac(6')-Ie-aph(2'')-Ia gene was identified by PCR technique. gentamicin resistant enterococci(GRE) were isolated from 76(15.2%) of 500 fecal samples. The isolated species were: E. faecalis 45(59.2%), E. faecium 29(38.1%) and E. gallinarum 2(2.63%). GRE isolates were highly resistant to gentamicin(MIC ≥ 500 μg/ml). Eleven different antimicrobial resistance patterns were observed in this study. All of isolates carried the aac(6')-Ie-aph(2'')-Ia resistance gene. These results represent a rather high prevalence of gentamicin resistance enterococci as a normal flora in the community. The aac(6')-Ie-aph(2'')-Ia gene was the most common gene among the gentamicinresistant isolates evaluated in this stud.