Increased cell wall teichoic acid production and D-alanylation are common phenotypes among daptomycin-resistant methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates

PLoS One. 2013 Jun 13;8(6):e67398. doi: 10.1371/journal.pone.0067398. Print 2013.

Abstract

Multiple mechanisms have been correlated with daptomycin-resistance (DAP-R) in Staphylococcus aureus. However, one common phenotype observed in many DAP-R S. Aureus strains is a thickened cell wall (CW). The first evidence for an impact of CW-linked glycopolymers on this phenotype was recently demonstrated in a single, well-characterized DAP-R methicillin-susceptible S. aureus (MSSA) strain. In this isolate the thickened CW phenotype was linked to an increased production and D-alanylation of wall teichoic acids (WTA). In the current report, we extended these observations to methicillin-resistant daptomycin-sensitive/daptomyin-resistant (DAP-S/DAP-R) strain-pairs. These pairs included methicillin-resistant S. aureus (MRSA) isolates with and without single nucleotide polymorphisms (SNPs) in mprF (a genetic locus linked to DAP-R phenotype). We found increased CW dry mass in all DAP-R vs DAP-S isolates. This correlated with an increased expression of the WTA biosynthesis gene tagA, as well as an increased amount of WTA in the DAP-R vs DAP-S isolates. In addition, all DAP-R isolates showed a higher proportion of WTA D-alanylation vs their corresponding DAP-S isolate. We also detected an increased positive surface charge amongst the DAP-R strains (presumably related to the enhanced D-alanylation). In comparing the detailed CW composition of all isolate pairs, substantive differences were only detected in one DAP-S/DAP-R pair. The thickened CW phenotype, together with an increased surface charge most likely contributes to either: i) a charge-dependent repulsion of calcium complexed-DAP; and/or ii) steric-limited access of DAP to the bacterial cell envelope target. Taken together well-defined perturbations of CW structural and functional metrics contribute to the DAP-R phenotype and are common phenotypes in DAP-R S. Aureus isolates, both MSSA and MRSA. Note: Although "daptomycin-nonsusceptibility" is the generally accepted terminology, we have utilized the term "daptomycin resistance" for ease of presentation in this manuscript.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Cell Wall / metabolism*
  • Daptomycin / pharmacology*
  • Drug Resistance, Multiple, Bacterial / genetics
  • Gene Expression Profiling
  • Gene Expression Regulation, Bacterial
  • Humans
  • Methicillin-Resistant Staphylococcus aureus / drug effects*
  • Methicillin-Resistant Staphylococcus aureus / genetics
  • Methicillin-Resistant Staphylococcus aureus / metabolism*
  • Microbial Sensitivity Tests
  • Peptidoglycan / chemistry
  • Peptidoglycan / metabolism
  • Phenotype*
  • Staphylococcal Infections / microbiology
  • Teichoic Acids / biosynthesis*

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Peptidoglycan
  • Teichoic Acids
  • Daptomycin