Emergence of methicillin-resistant Staphylococcus aureus with intermediateglycopeptide resistance - Clinical significance and treatment options

Methicillin-resistant Staphylococcus aureus is a pathogen that is associate d with serious infections that pose a significant risk of morbidity and mor tality because of their multidrug resistant nature. Until recently, therape utic options were limited to vancomycin, making the use of this drug widesp read. Unfortunately, the continued application of this drug has led to the emergence of glycopeptide intermediate susceptible S. aureus (GISA). By def inition, these organisms demonstrated a vancomycin minimum inhibitory conce ntration (MIC) of >4 mg/L and <32 mg/L. However, although the mechanism of resistance is not fully elucidated at this time, GISA strains have demonstr ated thickened or aggregated cell walls, an increase in penicillin binding proteins and greater autolytic activity. At present. the overall number of reported cases of GISA is relatively low. In most cases, thus far, prolonge d courses of vancomycin were reported. A few cases reported monitoring seru m vancomycin concentrations but because of limited information, no associat ion with outcome can be made. Whether these GISA strains will become more w idespread or evolve into fully glycopeptide resistant strains is unknown at this time. Although there are a number of new agents that possess activity against these pathogens, there is no consensus regarding specific recommen dations for treatment. Strict infection control practices, routine screenin g for resistance and controlled use of antibacterial agents, especially van comycin, are critical steps in preventing the further development of resist ance among staphylococci.