Signal Biosynthesis Inhibition with Ambuic Acid as a Strategy To Target Antibiotic-Resistant Infections

Antimicrob Agents Chemother. 2017 Jul 25;61(8):e00263-17. doi: 10.1128/AAC.00263-17. Print 2017 Aug.


There has been major interest by the scientific community in antivirulence approaches against bacterial infections. However, partly due to a lack of viable lead compounds, antivirulence therapeutics have yet to reach the clinic. Here we investigate the development of an antivirulence lead targeting quorum sensing signal biosynthesis, a process that is conserved in Gram-positive bacterial pathogens. Some preliminary studies suggest that the small molecule ambuic acid is a signal biosynthesis inhibitor. To confirm this, we constructed a methicillin-resistant Staphylococcus aureus (MRSA) strain that decouples autoinducing peptide (AIP) production from regulation and demonstrate that AIP production is inhibited in this mutant. Quantitative mass spectrometric measurements show that ambuic acid inhibits signal biosynthesis (50% inhibitory concentration [IC50] of 2.5 ± 0.1 μM) against a clinically relevant USA300 MRSA strain. Quantitative real-time PCR confirms that this compound selectively targets the quorum sensing regulon. We show that a 5-μg dose of ambuic acid reduces MRSA-induced abscess formation in a mouse model and verify its quorum sensing inhibitory activity in vivo Finally, we employed mass spectrometry to identify or confirm the structure of quorum sensing signaling peptides in three strains each of S. aureus and Staphylococcus epidermidis and single strains of Enterococcus faecalis, Listeria monocytogenes, Staphylococcus saprophyticus, and Staphylococcus lugdunensis By measuring AIP production by these strains, we show that ambuic acid possesses broad-spectrum efficacy against multiple Gram-positive bacterial pathogens but does not inhibit quorum sensing in some commensal bacteria. Collectively, these findings demonstrate the promise of ambuic acid as a lead for the development of antivirulence therapeutics.

Keywords: Agr system; Staphylococcus aureus; ambuic acid; inhibitors; virulence regulation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / pharmacology*
  • Bacterial Proteins / biosynthesis*
  • Cyclohexanones / chemistry
  • Cyclohexanones / pharmacology*
  • Disease Models, Animal
  • Gram-Positive Bacteria / drug effects*
  • Gram-Positive Bacteria / genetics
  • Gram-Positive Bacteria / pathogenicity
  • Gram-Positive Bacterial Infections / drug therapy*
  • Gram-Positive Bacterial Infections / microbiology
  • Humans
  • Male
  • Methicillin-Resistant Staphylococcus aureus / drug effects
  • Methicillin-Resistant Staphylococcus aureus / genetics
  • Methicillin-Resistant Staphylococcus aureus / pathogenicity
  • Mice
  • Mice, Inbred BALB C
  • Peptides, Cyclic / biosynthesis*
  • Quorum Sensing / drug effects
  • Signal Transduction
  • Staphylococcal Infections / drug therapy
  • Staphylococcal Infections / microbiology
  • Virulence Factors


  • AgrD protein, Staphylococcus
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Cyclohexanones
  • Peptides, Cyclic
  • Virulence Factors
  • ambuic acid