Evaluation of susceptibility of methicillin resistant Staphylococcus aureus strains to vancomycin

Susceptibility to vancomycin and teicoplanin was studied in the most frequently isolated Staphylococcus species isolated in the State Hospital Clinic Nr 1 in Warsaw in 1994. No strains resistant to vancomycin were found in two Staphylococci most frequently isolated from clinical material: S. aureus and S. epidermidis. Occurrence of this resistance is very rare and is restricted only to coagulase-negative Staphylococci such as S. xylosus, S. capitis, S. lentus and S. cohni. Resistance to teicoplanin was observed more often (1.4% in S. aureus and from 11.8% to 39.3% in 9 species of coagulase-negative Staphylococci). For the majority of methicillin-susceptible clinical strains (80%), the MBC value did not exceed 4.0 mcg/ml of vancomycin while for almost half of the strains in the population of methicillin-resistant strains MBC values ranged from 32.0 to 128 mcg/ml of vancomycin. Moreover, vancomycin-tolerant strains were found eight times more often in the studied MRSA (26.7%) population than in MSSA strains (3.3%).