title: Serial daptomycin selection generates daptomycin-nonsusceptible Staphylococcus aureus strains with a heterogeneous vancomycin-intermediate phenotype.
abstract: In order to better understand the mechanism of daptomycin resistance, we generated a daptomycin-nonsusceptible derivative strain, strain 10*3d1 (MIC = 3.0 microg/ml), by in vitro exposure of methicillin-resistant Staphylococcus aureus strain N315DeltaIP (MIC = 0.5 microg/ml) to daptomycin. We also obtained a daptomycin-susceptible phenotypic revertant strain, strain 10*3d1-10 (MIC = 1.0 microg/ml), by passaging 10*3d1 in drug-free medium for 10 days. The resultant triple-isogenic strains were analyzed for their phenotypes and gene expression by microarray analysis. No significant differences in the membrane fluidities of 10*3d1 and 10*3d1-10 compared to the membrane fluidity of N315DeltaIP were observed. Resistant strain 10*3d1 had the highest membrane potential, followed by strains 10*3d1-10 and N315DeltaIP. The vancomycin and teicoplanin MICs also increased. Teichoic acid genes (tagA, tagG), mprF encoding lysyl-phosphatidylglycerol, and cls encoding cardiolipin synthase were downregulated in 10*3d1 and 10*3d1-10. The vraF and vraG genes, which encode ATP binding cassette transporter proteins, were upregulated in 10*3d1. The vraSR two-component regulatory system was upregulated, and electron microscopy revealed that the cell wall of 10*3d1 was significantly thicker than that of the parental strain. Taken together, daptomycin exposure selected a daptomycin-nonsusceptible strain with a phenotype similar to that of heterogeneous vancomycin-intermediate S. aureus and a transcription profile that partially overlapped that of heterogeneous vancomycin-intermediate S. aureus.
authors.affiliation: Department of Bacteriology, Faculty of Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
authors.forename: Ilana Lopes Baratella da Cunha
authors.initials: IL
authors.lastname: Camargo
authors.forename: Hui-Min
authors.initials: HM
authors.lastname: Neoh
authors.forename: Longzhu
authors.initials: L
authors.lastname: Cui
authors.forename: Keiichi
authors.initials: K
authors.lastname: Hiramatsu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D017576:Daptomycin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D008560:Membrane Fluidity; D008564:Membrane Potentials / Q000187:drug effects; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D008826:Microbial Sensitivity Tests; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D014640:Vancomycin; D017576:Daptomycin