Resistance to Daptomycin in the Treatment of Methicillin Resistant Staphylococcus aureus Bacteremia

Abstract

Staphylococcus aureus is an aerobic gram positive bacterium that can cause harmful skin infections and bacteremia. Some strains of S. aureus have become resistant to synthetic penicillin (Methicillin) and therefore need to be treated with Daptomycin (Skiest 2006). Daptomycin is a novellipopeptide antibiotic that was approved by the Food and Drug Administration (FDA) for treatment of gram positive skin infections in 2003 (Hayden et al. 2005 and Marty et al. 2006). Daptomycin has been known to successfully combat gram-positive bacteria by quickly depolarizing the cells. Two patients at St. John Hospital & Medical Center (Detroit, MI) were on prolonged treatment of Daptomycin for S. aureus bacteremia and blood cultures showed non-susceptibility to the drug. The samples from these patients were collected and saved so that nonsusceptibility to Daptomycin treatment could be tracked over time using a microdilution technique to determine minimum inhibitory concentrations (MI Cs) of the drug. Using SCCmec typing and Pulsed Field Gel Electrophoresis (PFGE), strains of bacteria were compared and classified. Both patients' blood cultures were shown to develop nonsusceptibility to Daptomycin after 5 and 7 days of treatment. Clinically, this study shows that patients with S. aureus bacteremia treated with Daptomycin for prolonged periods of time should have their samples carefully monitored for non-susceptibility that may lead to failure of treatment.