Comprehensive Analysis of Phospholipids and Glycolipids in the Opportunistic Pathogen Enterococcus Faecalis

PLoS One. 2017 Apr 19;12(4):e0175886. doi: 10.1371/journal.pone.0175886. eCollection 2017.

Abstract

Enterococcus faecalis is a Gram-positive, opportunistic, pathogenic bacterium that causes a significant number of antibiotic-resistant infections in hospitalized patients. The development of antibiotic resistance in hospital-associated pathogens is a formidable public health threat. In E. faecalis and other Gram-positive pathogens, correlations exist between lipid composition and antibiotic resistance. Resistance to the last-resort antibiotic daptomycin is accompanied by a decrease in phosphatidylglycerol (PG) levels, whereas multiple peptide resistance factor (MprF) converts anionic PG into cationic lysyl-PG via a trans-esterification reaction, providing resistance to cationic antimicrobial peptides. Unlike previous studies that relied on thin layer chromatography and spectrophotometry, we have performed liquid chromatography-tandem mass spectrometry (LC-MS/MS) directly on lipids extracted from E. faecalis, and quantified the phospholipids through multiple reaction monitoring (MRM). In the daptomycin-sensitive E. faecalis strain OG1RF, we have identified 17 PGs, 8 lysyl-PGs (LPGs), 23 cardiolipins (CL), 3 glycerophospho-diglucosyl-diacylglycerols (GPDGDAG), 5 diglucosyl-diacylglycerols (DGDAG), 3 diacylglycerols (DAGs), and 4 triacylglycerols (TAGs). We have quantified PG and shown that PG levels vary during growth of E. faecalis in vitro. We also show that two daptomycin-resistant (DapR) strains of E. faecalis have substantially lower levels of PG and LPG levels. Since LPG levels in these strains are lower, daptomycin resistance is likely due to the reduction in PG. This lipidome map is the first comprehensive analysis of membrane phospholipids and glycolipids in the important human pathogen E. faecalis, for which antimicrobial resistance and altered lipid homeostasis have been intimately linked.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Biotransformation
  • Cardiolipins / classification
  • Cardiolipins / isolation & purification
  • Cardiolipins / metabolism
  • Chromatography, Liquid
  • Daptomycin / pharmacology*
  • Diglycerides / classification
  • Diglycerides / isolation & purification
  • Diglycerides / metabolism
  • Drug Resistance, Multiple, Bacterial / drug effects*
  • Drug Resistance, Multiple, Bacterial / physiology
  • Enterococcus faecalis / drug effects*
  • Enterococcus faecalis / growth & development
  • Enterococcus faecalis / metabolism
  • Lipid Metabolism
  • Lysine / classification
  • Lysine / isolation & purification
  • Lysine / metabolism*
  • Metabolomics
  • Phosphatidylglycerols / classification
  • Phosphatidylglycerols / isolation & purification
  • Phosphatidylglycerols / metabolism*
  • Tandem Mass Spectrometry
  • Triglycerides / classification
  • Triglycerides / isolation & purification
  • Triglycerides / metabolism

Substances

  • Anti-Bacterial Agents
  • Cardiolipins
  • Diglycerides
  • Phosphatidylglycerols
  • Triglycerides
  • lysylphosphatidylglycerol
  • Lysine
  • Daptomycin

Grant support

Authors RR, IHG, ZJN, and KAK were supported by the National Research Foundation and Ministry of Education Singapore under its Research Centre of Excellence Programme and by the National Research Foundation under its Singapore NRF Fellowship programme awarded to KAK (NRF-NRFF2011-11). ACG, JKK, LG, and MRW were supported by grants from the National University of Singapore via the Life Sciences Institute (LSI), the National Research Foundation (NRFI2015-05), and a BMRC-SERC joint grant (BMRC-SERC 112 148 0006) from the Agency for Science, Technology and Research (A*Star). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.