The Biomerieux Solution Did You Know? Practical Advice

The first S. aureus strain with a vancomycin MIC 8 mg/L was isolated in 1996 from a Japanese patient to whom vancomycin therapy was ineffective [1]. Subsequently, dozens of VRSA strains were isolated from USA, France, Korea, South Africa, Scotland and Brazil [2], indicating that the issue is a global one [3]. However, the real essence of the issue lies in the latent dissemination of «hetero-VRSA», which has lower MIC values than 8 mg/L, but is capable of generating VRSA at high frequency upon exposure to vancomycin. In 1997, we reported 23 Japanese MRSA strains with reduced susceptibility to vancomycin [4]. As is the case for methicillin resistance, we recognized two classes of phenotype in vancomycin resistance. One is vancomycin-resistant Staphylococcus aureus (VRSA) that is defined by a vancomycin MIC of 8 mg/l as measured by the broth-dilution susceptibility test. The nomenclature of VRSA is based on the British Society for Chemotherapy. The same strain is called vancomycin-intermediate S. aureus (VISA) or glycopeptideintermediate S. aureus (GISA) in the USA, according to American interpretation criteria for ■ When to suspect a VISA strain? ■ How to confirm? ■ Latest news