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

ABSTRACT

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.