Prevalence of high level aminoglycoside and vancomycin resistance among enterococci in Turkey

Enterococcus spp. have become the third most common cause of nosocomial infections. High-level aminoglycoside resistance (HLAR), an important clinical concern, has been associated with some species of enterococci. The synergistic effect obtained by the combination of aminoglycosides with penicillin or vancomycin disappears in strains that show high-level resistance (HLR) to the aminoglycosides. We evaluated the agar dilution and high content disk diffusion tests for the detection of HLAR for 60 isolated enterococci. In our study 4 strains of Enterococcus faecalis (6.6%) and 8 strains of Enterococcus faecium (13.3%), totally 20% were found to be highly resistant to gentamicin; 2 strains of E. faecalis (13.3%), 8 strains of E. faecium (3.3%), totally 16.6% showed HLR to streptomycin by agar dilution method and the same rates were found by high-content disk diffusion method. 2 strains of E. faecalis (3.3%), 4 strains of E. faecium (6.6%), totally 10% showed vancomycin resistance by agar dilution method. The ratio for beta lactamase activity was found to be 26.6% for E. faecalis and 3.3% for E. faecium. Our results demonstrate that high-content disk diffusion test should be performed by using both gentamicin and streptomycin in routine screening of HLAR among enterococci and the determination of beta lactamase activity at the same time is also useful for detecting resistance to a beta lactam agent.