Reduced vancomycin susceptibility in Staphylococcus aureus clinical isolates: a spectrum of less investigated uncertainties.

Background: Staphylococcus aureus clinical isolates with vancomycin MICs of 2 µg/ml have been associated with vancomycin therapeutic failure and the heterogenous vancomycin-intermediate S. aureus (hVISA) phenotype. While carriage of van genes has usually been associated with higher level of MIC and frank vancomycin resistance, the unrecognized risk of hetero-resistance is frequently underestimated.