Treatment of Infections Due to Methicillin-Resistant Staphylococcus aureus

Abstract

Strains of methicillin-resistant Staphylococcus aureus are resistant to other penicillins. The in-vitro susceptibility to the cephalosporins differs among strains. Some strains, susceptible to cephalosporins by the standard disk susceptibility test, are proved resistant by the quantitative dilution test; they may show pop-up colonies within the zone of inhibition when incubated further at room temperature. The clinical efficacy of the cephalosporins with or without an aminoglycoside in treating infections due to methicillin-resistant S. aureus is in doubt. To date, all strains of methicillin-resistant S. aureus have been susceptible to vancomycin. In-vitro antagonism of vancomycin and rifampin against S. aureus has been shown. Thus, vancomycin alone appears to be the treatment of choice; if this treatment fails, aminoglycoside or rifampin should be added. Serum bactericidal titers should be carefully monitored before and after the addition of the new agent and in-vitro time-kill studies of combination of antibiotics done if feasible.