Elucidation of the Mode of Action of a New Antibacterial Compound Active against Staphylococcus aureus and Pseudomonas aeruginosa

PLoS One. 2016 May 11;11(5):e0155139. doi: 10.1371/journal.pone.0155139. eCollection 2016.

Abstract

Nosocomial and community-acquired infections caused by multidrug resistant bacteria represent a major human health problem. Thus, there is an urgent need for the development of antibiotics with new modes of action. In this study, we investigated the antibacterial characteristics and mode of action of a new antimicrobial compound, SPI031 (N-alkylated 3, 6-dihalogenocarbazol 1-(sec-butylamino)-3-(3,6-dichloro-9H-carbazol-9-yl)propan-2-ol), which was previously identified in our group. This compound exhibits broad-spectrum antibacterial activity, including activity against the human pathogens Staphylococcus aureus and Pseudomonas aeruginosa. We found that SPI031 has rapid bactericidal activity (7-log reduction within 30 min at 4x MIC) and that the frequency of resistance development against SPI031 is low. To elucidate the mode of action of SPI031, we performed a macromolecular synthesis assay, which showed that SPI031 causes non-specific inhibition of macromolecular biosynthesis pathways. Liposome leakage and membrane permeability studies revealed that SPI031 rapidly exerts membrane damage, which is likely the primary cause of its antibacterial activity. These findings were supported by a mutational analysis of SPI031-resistant mutants, a transcriptome analysis and the identification of transposon mutants with altered sensitivity to the compound. In conclusion, our results show that SPI031 exerts its antimicrobial activity by causing membrane damage, making it an interesting starting point for the development of new antibacterial therapies.

MeSH terms

  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / metabolism
  • Biosynthetic Pathways / drug effects
  • Carbazoles / chemistry
  • Carbazoles / pharmacology
  • Cell Division / drug effects
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Cell Membrane Permeability / drug effects
  • Drug Resistance, Bacterial / drug effects
  • Fatty Acids / biosynthesis
  • Gene Expression Profiling
  • Gene Regulatory Networks / drug effects
  • Genes, Bacterial
  • Kinetics
  • Lipid Metabolism / drug effects
  • Lipid Metabolism / genetics
  • Liposomes / chemistry
  • Macromolecular Substances / metabolism
  • Microbial Sensitivity Tests
  • Microbial Viability / drug effects
  • Mutation / genetics
  • Phospholipids / metabolism
  • Pseudomonas aeruginosa / drug effects*
  • Pseudomonas aeruginosa / genetics
  • Sequence Analysis, DNA
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / genetics
  • Time Factors

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Carbazoles
  • Fatty Acids
  • Liposomes
  • Macromolecular Substances
  • Phospholipids

Grants and funding

This work was supported by the European Commission’s Seventh Framework Programme (FP7/2007-2013) under the grant agreement COATIM (project n° 278425), the Interuniversity Attraction Poles Programme initiated by the Belgian Science Policy Office and by the FWO (grants G.0413.10, G.0471.12N, G0B2515N to JM). KT acknowledges the receipt of a mandate of the ‘Industrial Research Fund’ of KU Leuven (IOFm/05/022). imec provided support in the form of salaries for author MF. The funders did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.