title: Phenotypic and genotypic characterization of daptomycin-resistant methicillin-resistant Staphylococcus aureus strains: relative roles of mprF and dlt operons.
abstract: Development of in vivo daptomycin resistance (DAP-R) among Staphylococcus aureus clinical isolates, in association with clinical treatment failures, has become a major therapeutic problem. This issue is especially relevant to methicillin-resistant S. aureus (MRSA) strains in the context of invasive endovascular infections. In the current study, we used three well-characterized and clinically-derived DAP-susceptible (DAP-S) vs. resistant (DAP-R) MRSA strain-pairs to elucidate potential genotypic mechanisms of the DAP-R phenotype. In comparison to the DAP-S parental strains, DAP-R isolates demonstrated (i) altered expression of two key determinants of net positive surface charge, either during exponential or stationary growth phases (i.e., dysregulation of dltA and mprF), (ii) a significant increase in the D-alanylated wall teichoic acid (WTA) content in DAP-R strains, reflecting DltA gain-in-function; (iii) heightened elaboration of lysinylated-phosphatidylglyderol (L-PG) in DAP-R strains, reflecting MprF gain-in-function; (iv) increased cell membrane (CM) fluidity, and (v) significantly reduced susceptibility to prototypic cationic host defense peptides of platelet and leukocyte origins. In the tested DAP-R strains, genes conferring positive surface charge were dysregulated, and their functionality altered. However, there were no correlations between relative surface positive charge or cell wall thickness and the observed DAP-R phenotype. Thus, charge repulsion mechanisms via altered surface charge may not be sufficient to explain the DAP-R outcome. Instead, changes in the compositional or biophysical order of the DAP CM target of such DAP-R strains (i.e., increased fluidity) may be essential to this phenotype. Taken together, DAP-R in S. aureus appears to involve multi-factorial and strain-specific adaptive mechanisms.
authors.affiliation: Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America; The David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America.
authors.forename: Nagendra N
authors.initials: NN
authors.lastname: Mishra
authors.affiliation: Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America; The David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America.
authors.forename: Arnold S
authors.initials: AS
authors.lastname: Bayer
authors.affiliation: Interfaculty Institute of Microbiology and Infection Medicine, University of Tübingen, Tübingen, Germany; German Center for Infection Research (DZIF), Tübingen, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Weidenmaier
authors.affiliation: Interfaculty Institute of Microbiology and Infection Medicine, University of Tübingen, Tübingen, Germany.
authors.forename: Timo
authors.initials: T
authors.lastname: Grau
authors.affiliation: Interfaculty Institute of Microbiology and Infection Medicine, University of Tübingen, Tübingen, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Wanner
authors.affiliation: Department of Biomedical Sciences-Microbiology, University of Catania, Catania, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Stefani
authors.affiliation: Department of Biomedical Sciences-Microbiology, University of Catania, Catania, Italy.
authors.forename: Viviana
authors.initials: V
authors.lastname: Cafiso
authors.affiliation: Department of Biomedical Sciences-Microbiology, University of Catania, Catania, Italy.
authors.forename: Taschia
authors.initials: T
authors.lastname: Bertuccio
authors.affiliation: Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America; The David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America; Division of Molecular Medicine, Harbor-UCLA Medical Center, Torrance, California, United States of America.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Yeaman
authors.affiliation: The David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America; Cedars-Sinai Medical Center, Los Angeles, California, United States of America.
authors.forename: Cynthia C
authors.initials: CC
authors.lastname: Nast
authors.affiliation: Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California, United States of America; The David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America.
authors.forename: Soo-Jin
authors.initials: SJ
authors.lastname: Yang
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology; D002473:Cell Wall / Q000378:metabolism; D017576:Daptomycin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D005227:Fatty Acids / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005838:Genotype; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009876:Operon; D010743:Phospholipids / Q000378:metabolism; D013682:Teichoic Acids / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D005227:Fatty Acids; D010743:Phospholipids; D013682:Teichoic Acids; D017576:Daptomycin