title: Plant phenolic compounds as ethidium bromide efflux inhibitors in Mycobacterium smegmatis.
abstract: BACKGROUND
  One-third of the world's population is infected with the dormant tuberculosis bacillus, and there have been no new antimycobacterial compounds with new modes of action for over 30 years. Extensively drug-resistant tuberculosis is resistant to first- and second-line drugs, which can have severe side effects, and requires the breakthrough of new antituberculotics and resistance-modifying agents. Efflux pumps can cause multidrug resistance and have recently evoked much interest as promising new targets in antimicrobial therapy.
  
  
  OBJECTIVE
  The study was performed to set up an ethidium bromide (EtBr) efflux assay in Mycobacterium smegmatis mc(2)155 for testing plant natural compounds as mycobacterial efflux pump inhibitors (EPIs).
  
  
  METHODS
  After determining the MICs of the putative EPIs, they were tested for synergistic effects with EtBr prior to the efflux assay.
  
  
  RESULTS
  We established an EtBr efflux assay in M. smegmatis mc(2)155. The isoflavone biochanin A exhibited efflux pump inhibiting activity comparable to that of verapamil. The flavone luteolin and the stilbene resveratrol were less active.
  
  
  CONCLUSIONS
  A new assay was established to observe the EtBr efflux in M. smegmatis and was applied to evaluate plant phenolic compounds. Our results highlighted that the isoflavonoid biochanin A exhibited better EPI activities than other flavonoids in mycobacteria.
authors.affiliation: Institute of Pharmaceutical Sciences, Department of Pharmacognosy, Karl-Franzens-University of Graz, Universitaetsplatz 4/I, A-8010 Graz, Austria.
authors.forename: Doris
authors.initials: D
authors.lastname: Lechner
authors.forename: Simon
authors.initials: S
authors.lastname: Gibbons
authors.forename: Franz
authors.initials: F
authors.lastname: Bucar
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000032:analysis*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004996:Ethidium / Q000378:metabolism / Q000494:pharmacology*; D019833:Genistein / Q000494:pharmacology; D047311:Luteolin / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D020102:Mycobacterium smegmatis / Q000187:drug effects*; D010636:Phenols / Q000494:pharmacology*; D000077185:Resveratrol; D013267:Stilbenes / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D026901:Membrane Transport Proteins; D010636:Phenols; D013267:Stilbenes; D014700:Verapamil; D019833:Genistein; D004996:Ethidium; D047311:Luteolin; D000077185:Resveratrol; C004541:biochanin A