Combination Effects of Various Beta-Lactam Antibiotics with Vancomycin or Teicoplanin against Staphylococcus aureus with Reduced Susceptibility to Vancomycin / 대한진단검사의학회지

ABSTRACT

BACKGROUND: Combination effects of various beta-lactam antibiotics with vancomycin or teicoplanin against methicillin-resistant Staphylococcus aureus (MRSA) that were detected as pos-sible hetero-vancomycin resistant Staphylococcus aureus (hetero-VRSA) by the Mu-3 agar method, were evaluated. METHODS: Twenty-four strains of MRSA (possible hetero-VRSA) from 22 inpatients of Dankook University Hospital from July through November 1998, were subjected to the study. Minimum inhibitory concentrations (MICs) of antibiotics, alone or in combination, were tested with the agar dilution method and the fractional inhibitory concentration (FIC) indices were calculated to estimate the combination effects. RESULTS: Six strains of 24 MRSA were estimated as hetero-VRSA by population analysis. The aver-age FIC index of imipenem (I), flomoxef (F), cephalothin (C), cefpirome (E) in combination with van-comycin (V) and teicoplanin (T) were 0.584 for I-V, 0.200 for I-T, 0.747 for F-V, 0.230 for F-T, 0.633 for C-V, 0.374 for C-T, 0.773 for E-V, and 0.386 for E-T, respectively. The presence of synergy and addi-tivity in beta-Lactams were observed as 5.3% (16/304) and 90.1% (274/304) for the combination of van-comycin with I, F, C, or E, respectively, and 29.3% (164/560) and 69.8% (391/560) for the combina-tion of teicoplanin with I, F, C, or E, respectively. CONCLUSIONS: We concluded that the selected beta-lactam antibiotics with vancomycin or teicoplanin showed effective against possible hetero-VRSA, as the combination effects were syner-gistic or additive with the average of the FIC index and the frequency of synergy and additivity in this study.