Clinical relevance of increasing glycopeptide MICs against Staphylococcus aureus.

Glycopeptides are among the most widely used agents for the treatment of serious infections caused by Gram-positive bacteria, with vancomycin recommended for the treatment of infections caused by beta-lactam-resistant Staphylococcus aureus (MRSA). However, the utility of glycopeptides against MRSA has come into question owing to their poor tissue penetration, slow bactericidal activity and the emergence of strains with reduced susceptibility. A number of single-centre studies have demonstrated incremental increases in glycopeptide MICs for S. aureus strains over time - a phenomenon known as glycopeptide creep. High MICs have long been known to correlate with poorer clinical outcomes, but recent studies have shown that even small increases in MIC below the susceptibility breakpoint can affect the clinical efficacy of glycopeptides. The accurate measurement and ongoing surveillance of glycopeptide MICs at individual sites is therefore recommended to assist clinicians in their choice of empiric therapy for suspected serious S. aureus infections.