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

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.

Prevalence of Staphylococcus aureus with Reduced Susceptibility to Vancomycin in a Tertiary Hospital / 감염

BACKGROUND: Recently isolates of S. aureus with intermediate (VISA) and heterogeneous resistance (hetero-VRSA) to vancomycin, which has been the only effective against MRSA infections, were identified. Several infections due to these isolates did not respond to adequate antibiotic treatments. In Japan, the prevalences of hetero-VRSA ranged from 0 to 48%. The aim of this study was to determine the prevalence of S. aureus heterogenously resistant to vancomycin and VISA. METHODS: The isolates were collected at Seoul National University Hospital from April 1998 to August 1999. To detect S. aureus with reduced susceptibility to vancomycin, brain heart infusion (BHI) agar with 4 mg/L of vancomycin and Mu-3 agar were used. Analysis of resistant subpopulations of bacteria (population analysis) was done. Minimum inhibitory concentration (MIC) for vancomycin was determined by microbroth and agar dilution methods, respectively according to NCCLS and Hiramatsu's recommendation. Coagulase type was determined with type I-VIII antisera. RESULTS: Total 235 MRSA, including 88 isolates from blood and 147 from other specimens, were collected. After 88 blood isolates were inoculated on BHI agar with 4 mg/L of vancomycin, 14 isolates (16 %) grew in variable colonies. But there were no subclones with vancomycin MIC > or =8 mg/L on population analysis and no isolates which grew confluently on Mu-3 agar with beta-lactam disks. In addition, 147 isolates from other specimens did not grow confluently on Mu-3 agar. Among 64 MRSA and 32 MSSA isolates, coagulase type II (49, 77%) and Vll(8, 25%) were respectively the most common types. CONCLUSION: In our tertiary-care hospital, there were no MRSA isolates with reduced susceptibilities to vancomycin.

Vancomycin-resistant Staphylococcus aureus / 대한임상미생물학회지

Clinical isolates of Staphylococcus aureus with reduced susceptibility to vancomycin(VRSA) have been reported from Japan, the United States and France Although the isolates are considered intermediately resistant according to the National Committee for Clinical Laboratory Standards(NCCLS), they are already a cause of a serious concern in the ever worsening antibiotic crisis of today, because they are all methicillin-resistant S. aureus(MRSA) and they are isolated after prolonged and unsuccessful vancomycin therapy. Furthermore, a study in Japan showed a high prevalence of "hetero-VRSA", MRSA strains that are susceptible to vancomycin according to NCCLS, but contain subpopulation of VRSA at the frequency of > or =10-6 and thus can be converted easily to full-blown VRSA upon exposure to the antibiotic. Recent reports from Seoul showed that hetero-VRSA is also prevalent in Korea. This review is to examine the epidemiology, clinical significance, mechanisms and laboratory detection of vancomycin resistance in clinical isolates of S. aureus; and to summerize infection control guidelines recommended by Centers for Disease Control and Prevention and others for this newly emerging nosocomial pathogen.