Investigation of reduced glycopeptid susceptibility among methicillin resistant staphylococci

Incidence of vancomycin intermediate Staphylococcus aureus (VISA) and vancomycin hetero-intermediate Staphylococcus aureus (h-VISA) has been increasing in the world and our country. We aimed to determine whether there is any difference between the minimal inhibitory concentration (MIC) of glycopeptide antibiotics against meticillin susceptible and resistant staphylococci and investigate the prevalence of VISA and h-VISA among Staphylococcus aureus strains. 60 MRSA, MSSA, MRCNS and MSCNS isolated in our laboratory between April 2007-2008, were included in this study. Bacteria were inoculated onto a BHI agar supplemented with 6 mu g/ml vancomycin, strains which have shown growth on screen agar were evaluated for being VISA/hVISA by determining PAP-AUC ratio. Vancomycin and teicoplanin MIC values of the strains were determined by microdilution and E-test methods. Two of MRSA strains which grew on screen agar were excepted as suspicious VISA/h-VISA and they were confirmed as h-VISA by PAP-AUC method. Among all strains, methicillin resistant strains showed higher MIC values for glycopeptides than methicillin susceptible strains. We suggested that clinicians should be aware of h-VISA and VISA strains which are being increasingly reported in the world. More clinically supported multisentric studies must be performed in our country to clarify these prevalence rates and determine the clinical relevance of this resistance profile.