[Clinical relevance of hetero-VRSA in surgical infections]

Vancomycin was used increasingly for treating methicillin-resistant Staphylococcus aureus(MRSA) infection. Recently MRSA strains which showed low-level resistance to vancomycin were isolated. Vancomycin-intermediate Staphylococcus aureus(VISA) show a vancomycin minimum inhibitory concentration(MIC) of 8 micrograms/ml. VISA appear to be rare. The vancomycin resistance phenotype is reported to be unstable in such isolates. To detect heterogeneously resistant VRSA(hetero-VRSA. MIC 1 to 4 micrograms/ml), we need to use population analysis and growth on Mu3 agar plate, because MIC cannot confirm hetero-VRSA. Hetero-VRSA is not so rare(about 0-47%). Hetero-VRSA may be responsible for failure of vancomycin therapy, but its mechanism remains unclear. Until it becomes better understood, the clinical relevance cannot be assessed.