Can routine susceptibility tests detect VISA and VRSA?
Not all susceptibility testing methods detect VISA and VRSA isolates. Three out of six confirmed VRSA isolates were not reliably detected by automated testing systems in a recent report. Subsequently, some manufacturers have optimized their systems for VRSA detection, so laboratories should check with manufacturers to determine if their system has FDA clearance for VRSA detection. VRSA are detected by reference broth microdilution, agar dilution, Etest®, MicroScan® overnight and Synergies plus™; BD Phoenix™ system, disk diffusion, and the vancomycin screen agar plate [brain heart infusion (BHI) agar containing 6 µg/ml of vancomycin]. VISA isolates are not detected by disk diffusion. Methods that typically detect VISA are non-automated MIC methods including reference broth microdilution, agar dilution, and Etest® using a 0.5 McFarland standard to prepare inoculum. Automated methods and vancomycin screen agar plates usually detect VISA for which the vancomycin MICs are 8 µg/ml, but furth
