High-level Aminoglycoside Resistance and Reduced Susceptibility to Vancomycin in Nosocomial Enterococci

OBJECTIVES: The objectives of the present study were to identify the species of enterococci isolated from nosocomial infections and to determine the antibiotic susceptibility pattern with reference to high-level aminoglycosides and vancomycin. MATERIALS AND METHODS: Enterococci were isolated from various clinical samples collected from patients after 72 hours of hospitalization. Various species of Enterococcus were identified by standard methods. High-level aminoglycoside resistance and vancomycin susceptibility in enterococci were detected by disk-diffusion and agar-screen methods. RESULTS: One hundred eighty enterococcal strains were isolated from various clinical samples. Various species of Enterococcus — Enterococcus fecalis 130 (72.22%), Enterococcus casseliflavus 24 (13.33%), Enterococcus fecium 17 (9.44%), Enterococcus durans 7 (3.89%) and Enterococcus dispar 2 (1.11%) — were isolated. The highest resistance to aminoglycoside was observed among E. fecium, followed by E. durans, E. fecalis and E. casseliflavus, both by disk-diffusion and agar-screen methods. The high-level aminoglycoside resistance (HLAR) was significantly (P<0.05) higher in E. fecium by agar-screen method. All enterococci showed minimum inhibitory concentration (MIC) of ≤8 μg/mL to vancomycin. Sixteen (12.31%) E. fecalis and 3 (12.5%) E. fecium strains were intermediately resistant to vancomycin (MIC= 8 μg/mL), whereas other strains were susceptible to vancomycin. CONCLUSION: The occurrence of high-level aminoglycoside resistance in enterococcal isolates in our setup was high. Even though none of the enterococcal strains showed resistance to vancomycin, yet reduced susceptibility to vancomycin was noticed in our study. This would require routine testing of enterococcal isolates for HLAR and vancomycin susceptibility. Agar-screen method was found to be superior to disk-diffusion method in detecting resistant strains to aminoglycosides and vancomycin.