A quinolinol-based small molecule with anti-MRSA activity that targets bacterial membrane and promotes fermentative metabolism

J Antibiot (Tokyo). 2017 Oct;70(10):1009-1019. doi: 10.1038/ja.2017.79. Epub 2017 Jul 12.

Abstract

In a loss-of-viability screen of small molecules against methicillin-resistant Staphylococcus aureus (MRSA) USA300, we found a small molecule, designated DNAC-2, which has an MIC of 8 μg ml-1. DNAC-2 is a quinolinol derivative that is bactericidal at 2X MIC. Macromolecular synthesis assays at 2 × MIC of DNAC-2 revealed inhibition of DNA, cell wall, RNA and protein synthesis within fifteen to thirty minutes of treatment when compared to the untreated control. Transmission electron microscopy of DNAC-2-treated cells revealed a significantly thicker cell wall and impaired daughter cell separation. Exposure of USA300 cells to 1 × MIC of DNAC-2 resulted in mislocalization of PBP2 away from the septum in an FtsZ-independent manner. In addition, membrane localization with FM4-64, as well as depolarization study with DiOC2 and lipophilic cation TPP+ displayed membrane irregularities and rapid membrane depolarization, respectively, in DNAC-2-treated cells vs -untreated control. However, DNAC-2 exhibited almost no toxicity toward eukaryotic membranes. Notably, DNAC-2 drives energy generation toward substrate level phosphorylation and the bacteria become more sensitive to DNAC-2 under anaerobic conditions. We propose that DNAC-2 affects USA300 by targeting the membrane, leading to partial membrane depolarization and subsequently affecting aerobic respiration and energy-dependent functional organization of macromolecular biosynthetic pathways. The multiple effects may have the desirable consequence of limiting the emergence of resistance to DNAC-2.

MeSH terms

  • Anaerobiosis
  • Anti-Bacterial Agents / pharmacology*
  • Cell Membrane / drug effects*
  • Cell Wall / ultrastructure
  • Fermentation
  • Hydroxyquinolines / pharmacology*
  • Membrane Potentials
  • Methicillin-Resistant Staphylococcus aureus / drug effects*
  • Methicillin-Resistant Staphylococcus aureus / physiology
  • Methicillin-Resistant Staphylococcus aureus / ultrastructure
  • Microbial Sensitivity Tests
  • Microbial Viability / drug effects
  • Microscopy, Electron, Transmission
  • Time Factors

Substances

  • Anti-Bacterial Agents
  • Hydroxyquinolines