A Novel Mechanism of Inactivating Antibacterial Nitro Compounds in the Human Pathogen Staphylococcus aureus by Overexpression of a NADH-Dependent Flavin Nitroreductase

Antimicrob Agents Chemother. 2018 Jan 25;62(2):e01510-17. doi: 10.1128/AAC.01510-17. Print 2018 Feb.


Recently, the nitro-substituted bisquaternary bisnaphthalimides were reported to have substantial anti-infective activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Here, we selected resistant S. aureus clones by cultivation in increasing concentrations of the most active compound, MT02. Interestingly, MT02-resistant variants induced a diffusible red color of the broth. Chromatographic and spectroscopic investigations revealed a stepwise reduction of the bisquaternary bisnaphthalimides' nitro groups to amino groups. The corresponding derivatives were completely inactive against staphylococci. RNA sequencing experiments revealed a strong overexpression of a novel oxidoreductase in MT02-resistant strains. Deletion mutants of this enzyme did not produce the red color and were not able to develop resistance against bisquaternary bisnaphthalimides. Biochemical reactions confirmed an NADH-dependent deactivation of the nitro-substituted compounds. Thus, this is the first report of a nitroreductase-based antibiotic resistance mechanism in the human pathogen S. aureus.

Keywords: Staphylococcus aureus; antibacterial nitro compounds; bacterial nitroreductases; bacterial resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amines / chemistry
  • Amines / metabolism
  • Anti-Bacterial Agents / metabolism*
  • Anti-Bacterial Agents / pharmacology
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Biotransformation / genetics
  • Color
  • Culture Media / chemistry
  • Drug Resistance, Bacterial / genetics*
  • Gene Deletion
  • Gene Expression
  • Humans
  • Inactivation, Metabolic / genetics*
  • Methicillin-Resistant Staphylococcus aureus / drug effects
  • Methicillin-Resistant Staphylococcus aureus / genetics*
  • Methicillin-Resistant Staphylococcus aureus / metabolism
  • Microbial Sensitivity Tests
  • NAD / metabolism
  • Naphthalimides / metabolism*
  • Naphthalimides / pharmacology
  • Nitro Compounds / chemistry
  • Nitro Compounds / metabolism
  • Nitroreductases / deficiency
  • Nitroreductases / genetics*
  • Oxidation-Reduction


  • Amines
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Culture Media
  • Naphthalimides
  • Nitro Compounds
  • NAD
  • Nitroreductases
  • flavin nitroreductase