Antibiotic Susceptibility Levels of Clinical Enterococcus spp. Strains, Including Those Resistant to Glycopeptides and High Concentrations of Aminoglycosides

Background. The increased proportion of enterococci in infections and their growing resistance to antibiotics call for the need to ensure constant monitoring of the microorganisms’ sensitivity. Objectives. To assess the degree of sensitivity of clinical Enterococcus species to antibiotics. Material and Methods. The MIC values of five antibiotics (ampicillin, tetracycline, norfloxacin, vancomycin, teicoplanin) were determined using the agar dilution method and the E-test for 300 Enterococcus strains, including 191 E. faecalis and 109 E. faecium strains. Enterococcal resistance to high concentrations of gentamicin was determined using the disk-diffusion method. Results. Among the 300 tested Enterococcus strains there were 28 glycopeptide-resistant enterococci (GRE) strains (9.3%), including 26 E. faecium and 2 E. faecalis strains; 57.6% of the strains were high-level gentamicin resistant (HLGR) strains, constituting 85% of the E. faecium group and 42% of the E. faecalis group. The MIC50 and MIC90 values (in μg/ml) of the five tested antibiotics for the E. faecalis and E. faecium strains were, respectively, ampicillin: 0.5 and 2 (E. faecalis), 12 and > 256 (E. faecium); tetracycline: 32 and 128, 1 and 12; norfloxacin: 4 and 256, > 256 and > 256; vancomycin: 1 and 2, 2 and 256; and teicoplanin: 0.5 and 1, 0.75 and 3. The MICs of vancomycin and teicoplanin of the GRE strains were, respectively, ≥128 and ≥32 for E. faecium and > 256 and ≥ 48 for E. faecalis. Conclusions. The considerable sensitivity of the E. faecium strains to tetracycline, including also GRE and HLGR strains, creates a possibility to use antibiotics of the tetracycline group in the treatment of infections caused by strains of that species (Adv Clin Exp Med 2010, 19, 2, 155–162).