Modified PAP method to detect heteroresistance to vancomycin among methicillin resistant Staphylococcus aureus isolates at a tertiary care hospital.

This study was an attempt at developing, establishing, validating and comparing the modified PAP method for detection of hetero-vancomycin resistant Staphylococcus aureus (h-VRSA) with the routine antimicrobial susceptibility testing (using the BSAC standardized disc diffusion method), minimum inhibitory concentrations of vancomycin using standard E-test methodology and the Hiramatsu's screening method. A total of 50 methicillin resistant Staphylococcus aureus obtained from various clinical specimens, along with the Mu 3 and Mu 50 strains as controls, were studied. No VRSA isolates were obtained. However, four of the test strains were positive by the Hiramatsu's screening method, of which only one isolate could be confirmed by the modified PAP analysis method. This isolate was a coloniser from the drain fluid of a liver transplant recipient. The sensitivity, specificity, positive predictive value and the overall efficiency of the Hiramatsu's screening method with the modified PAP analysis as the gold standard were found to be 100, 93.8, 25 and 94%, respectively. It is very essential for clinical laboratories to screen for h-VRSA, given the increasing use of glycopeptide antibiotics in therapy and the potential for failed therapy in patients infected with these strains.