Detection of vancomycin resistant Staphylococcus aureus: a comparative study of three different phenotypic screening methods.

The objective of this study was to investigate screening methodologies, to detect Staphylococcus aureus strains with decreased susceptibility to vancomycin. Three methods were used to screen 160 Staphylococcus aureus clinical isolates along with ATCC quality control strains. Subsequently, MIC of all these 160 strains were determined by NCCLS methodology. The MIC of all the 160 clinical isolates was < or = 4 microg/mL and were classified as vancomycin susceptible by NCCLS criteria but 23 strains were positive by Hiramatshu method, two grew on MHA (5 microg/mL vancomycin) while CDC method correctly identified no vancomycin intermediate S.aureus (VISA) or vancomycin resistant S.aureus (VRSA) strains with reference to there MIC. CDC method was found to be the most appropriate screening methodology for detection of VISA or VRSA for diagnostic laboratories.