Background: Staphylococcus aureus is a species of bacteria that causes a number of diseases and more than 60% of it is presently resistant to methicillin. Vancomycin is the drug of choice for the eradication of methicillin-resistant S. aureus (MRSA).
Objective: This study aimed to investigate the susceptibility of heterogeneous vancomycin intermediate S. aureus (hVISA) and vancomycin intermediate S. aureus (VISA) to vancomycin by standard disk diffusion, microbroth dilution, a one-point population assay, and a population analysis profile.
Material and Method: Sixty-eight MRSA isolates from patients admitted to Sanprasitthiprasong Hospital between November 2010 and November 2011 were tested.
Results: Standard disk diffusion showed that all the MRSA isolates were susceptible to vancomycin. Vancomycin MICs for all isolates were 1-2 μg/mL. Only two MRSA isolates (2.9%) were able to grow on brain heart infusion agar supplemented with vancomycin 4 μg/mL and were confirmed by a population analysis as hVISA.
Conclusion: This study showed the effect of vancomycin on MRSA and the need for early detection and controlled planning.

Keywords: Methicillin-resistant Staphylococcus aureus (MRSA), Vancomycin, Heterogeneous vancomycin-intermediate S. aureus (hVISA), Vancomycin-intermediate S. aureus (VISA), High level vancomycin-resistant S. aureus (VRSA)