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Mannitol utilisation is required for protection of Staphylococcus aureus from human skin antimicrobial fatty acids

John G Kenny1, Josephine Moran, Stacey L Kolar

  • 1Institute of Integrative Biology, University of Liverpool, Liverpool, Merseyside, United Kingdom.

Plos One
|July 18, 2013
PubMed

Insights

Staphylococcus aureus uses mannitol fermentation as a key identifier. Inactivating the mtlD gene reduces survival against linoleic acid by altering metabolite accumulation.

Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Metabolic Engineering

Background:

  • Mannitol (Mtl) fermentation and acid production are characteristic of Staphylococcus aureus, differentiating it from other staphylococci.
  • The mtlD gene encodes Mannitol-1-Phosphate (Mtl-1-P) dehydrogenase, crucial for mannitol metabolism.
  • Linoleic acid is an antimicrobial fatty acid that targets bacterial membranes.

Purpose of the Study:

  • To investigate the role of mtlD in Staphylococcus aureus survival, particularly in the presence of linoleic acid.
  • To understand the metabolic consequences of mtlD inactivation.
  • To assess the impact of mtlD on hydrogen peroxide (H2O2) susceptibility and virulence.

Main Methods:

  • Gene inactivation (mtlD deletion mutant) and complementation.
  • Growth assays in the presence of linoleic acid.
  • Metabolite analysis using chromatography.
  • Determination of Minimum Inhibitory Concentration (MIC) for H2O2.
  • In vivo virulence testing in a septic arthritis model.

Main Results:

  • Inactivation of mtlD significantly reduced Staphylococcus aureus survival in the presence of linoleic acid.
  • The mtlD mutant accumulated high levels of Mannitol (Mtl) and Mannitol-1-Phosphate (Mtl-P) during growth.
  • Mtl-P accumulation was specific to the mtlD mutant, not observed in parent or full operon deletion strains.
  • The mtlD mutant showed decreased resistance to hydrogen peroxide (H2O2).
  • Virulence in a septic arthritis model remained unaffected by mtlD inactivation.

Conclusions:

  • The mtlD gene and its product are critical for Staphylococcus aureus resistance to linoleic acid, suggesting a potentiating role for mannitol metabolism in antimicrobial susceptibility.
  • Altered intracellular metabolite levels, specifically Mtl-P accumulation, are linked to reduced survival against membrane-acting antimicrobials.
  • While mtlD affects H2O2 susceptibility, it does not appear to be essential for virulence in the tested septic arthritis model.

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