[Detection methods for drug-resistant bacteria in routine examination--VISA]

Abstract

MRSA strains which clinically showed low-level resistance to vancomycin(VISA, hetero-VRSA) were isolated. Vancomycin-intermediate Staphylococcus aureus(VISA) was found to show a vancomycin minimum inhibitory concentration(MIC) of 8 to 16 micrograms/ml. The subpopulation of hetero vancomycin resistant MRSA(hetero-VRSA) was resistant to vancomycin MIC of 1 to 4 micrograms/ml. VISA and hetero-VRSA did not have vanA, vanB, vanC genes from vancomycin-resistant enterococci(VRE). The disk diffusion test could not detect VISA and hetero-VRSA. The MIC tests can confirm VRSA well. To detect the hetero-VRSA, we need to use population analysis and growth on hetero-VRSA agar (MU3 agar plate).