Optimizing the detection of methicillin-resistant Staphylococcus aureus with elevated vancomycin minimum inhibitory concentrations within the susceptible range Cameron J Phillips,1–3 Nicholas A Wells,4 Marianne Martinello,4 Simon Smith,4 Richard J Woodman,5 David L Gordon2,4 1SA Pharmacy, Flinders Medical Centre, Bedford Park, SA, Australia; 2Department of Microbiology and Infectious Diseases, School of Medicine, Flinders University, Adelaide, SA, Australia; 3School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, SA, Australia; 4SA Pathology, Microbiology and Infectious Diseases, Flinders Medical Centre, Bedford Park, SA, Australia; 5Flinders Centre for Epidemiology and Biostatistics, School of Medicine, Flinders University, Adelaide, SA, Australia Background: Determination of vancomycin minimum inhibitory concentration (MIC) can influence the agent used to treat methicillin-resistant Staphylococcus aureus (MRSA) infection. We studied diagnostic accuracy using E-test and Vitek-2 against a gold standard broth microdilution (BMD) methodology, the correlation between methods, and associations between vancomycin MIC and MRSA phenotype from clinical isolates.Methods: MRSA isolates were obtained from April 2012 to December 2013. Vancomycin MIC values were determined prospectively on all isolates by gradient diffusion E-test and automated Vitek-2. The Clinical and Laboratory Standards Institute reference BMD method was performed retrospectively on thawed frozen isolates. Diagnostic accuracy for detecting less susceptible strains was calculated at each MIC cutoff point for E-Test and Vitek2 using BMD ≥1 µg/mL as a standard. The correlation between methods was assessed using Spearman’s rho (Ρ). The association between MRSA phenotype and MIC for the three methods was assessed using Fisher’s exact test.Results: Of 148 MRSA isolates, all except one (E-te