title: Correlation of daptomycin bactericidal activity and membrane depolarization in Staphylococcus aureus.
abstract: The objective of this study was to further elucidate the role of membrane potential in the mechanism of action of daptomycin, a novel lipopeptide antibiotic. Membrane depolarization was measured by both fluorimetric and flow cytometric assays. Adding daptomycin (5 micro g/ml) to Staphylococcus aureus gradually dissipated membrane potential. In both assays, cell viability was reduced by >99% and membrane potential was reduced by >90% within 30 min of adding daptomycin. Cell viability decreased in parallel with changes in membrane potential, demonstrating a temporal correlation between bactericidal activity and membrane depolarization. Decreases in viability and potential also showed a dose-dependent correlation. Depolarization is indicative of ion movement across the cytoplasmic membrane. Fluorescent probes were used to demonstrate Ca(2+)-dependent, daptomycin-triggered potassium release from S. aureus. Potassium release was also correlated with bactericidal activity. This study demonstrates a clear correlation between dissipation of membrane potential and the bactericidal activity of daptomycin. A multistep model for daptomycin's mechanism of action is proposed.
authors.affiliation: Cubist Pharmaceuticals, Inc., Lexington, Massachusetts 02421, USA. jared.silverman@cubist.com
authors.forename: Jared A
authors.initials: JA
authors.lastname: Silverman
authors.forename: Nancy G
authors.initials: NG
authors.lastname: Perlmutter
authors.forename: Howard M
authors.initials: HM
authors.lastname: Shapiro
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003470:Culture Media; D017576:Daptomycin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005470:Fluorometry; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D017576:Daptomycin; D011188:Potassium