Expression and detection of hetero-vancomycin resistance in Staphylococcusaureus

Isolates of Staphylococcus aureus resistant to vancomycin have been reporte d but appear to be extremely rare. However, isolates displaying hetero-resi stance to vancomycin (hVRSA) are reportedly common in parts of Japan (9.3% of MRSA isolated from a group of university hospitals). We have investigate d the reliability of the proposed method for detection of hetero-resistant isolates and the ability of clinical S. aureus isolates to express vancomyc in resistance. The original method for identification of hVRSA was found to have poor reproducibility and may select for, rather than detect, vancomyc in resistance. There appears to be a spectrum of heterogeneity in the expre ssion of resistance to vancomycin among S. aureus. Until there is a clearer understanding of the mechanism and control of vancomycin resistance in S. aureus, and reliable tests are devised, the clinical relevance of different degrees of hetero-resistance cannot be assessed.