Journal Article

Phenotypic and Genotypic Characterization of Daptomycin-Resistant Methicillin-Resistant Staphylococcus aureus Strains: Relative Roles of mprF and dlt Operons

Weidenmaier, Christopher, Yeaman, Michael R., Mishra, Nagendra N., Cafiso, Viviana, Wanner, Stefanie, Yang, Soo-Jin, Grau, Timo, Bertuccio, Taschia, Nast, Cynthia C., Bayer, Arnold S., Stefani, Stefania

2014

Overview

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.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Anti-Bacterial Agents - pharmacology / Antibiotics / Antimicrobial Cationic Peptides - pharmacology / Biology and Life Sciences / Biomedical research / Cardiovascular system / Cell surface / Cell Wall - metabolism / Cell walls / Clinical isolates / Daptomycin / Daptomycin - pharmacology / Drug resistance / Drug Resistance, Bacterial / Fatty acids / Fatty Acids - metabolism / Fluidity / Gene expression / Gene Expression Regulation, Bacterial / Genotype / Genotype & phenotype / Humans / Hypotheses / Infectious diseases / Leukocytes / Medicine / Methicillin / Methicillin-Resistant Staphylococcus aureus - drug effects / Methicillin-Resistant Staphylococcus aureus - genetics / Methicillin-Resistant Staphylococcus aureus - metabolism / Microbial Sensitivity Tests / Neutrophils / Nosocomial infections / Operon / Operons / Peptides / Phospholipids - metabolism / Staphylococcus aureus / Staphylococcus infections / Strains (organisms) / Surface charge / Teichoic Acids - metabolism / Viscosity / Wall thickness