title: Anti-staphylococcal activity and mode of action of clofazimine.
abstract: OBJECTIVE
  Infections caused by Staphylococcus aureus might be treated with agents whose primary indications are for other infections. Clofazimine, an established anti-mycobacterial drug, could be such a candidate. However, the anti-staphylococcal properties of clofazimine have not been fully described and its mode of action, possibly involving inhibition of both RNA polymerase and a membrane-located target, has not been explored in detail. We have now conducted experiments to address these issues.
  
  
  METHODS
  Using established procedures, we examined the activity of clofazimine against a range of clinical isolates of S. aureus and determined whether it was bactericidal, exhibited a post-antibiotic effect (PAE), or interacted synergically with other agents. The potential for emergence of clofazimine-resistant mutants was also examined. Mode of action studies involved macromolecular synthesis assays, cross-screening against rifampicin-resistant mutants, susceptibility of RNA polymerase to clofazimine in vitro and several methods to detect drug-induced membrane damage.
  
  
  RESULTS
  Clofazimine demonstrated good anti-staphylococcal activity encompassing MSSA, MRSA and GISA. It was bactericidal and resistant mutants could not be isolated. Clofazimine did not exhibit a PAE and failed to act synergically with other drugs. No evidence for specific inhibition of RNA polymerase was obtained. Clofazimine caused non-specific inhibition of DNA, RNA and protein synthesis, consistent with membrane-damaging activity that was detected in three independent assays for membrane disrupting agents.
  
  
  CONCLUSIONS
  Clofazimine is a potent anti-staphylococcal agent. It appears to be a membrane-disrupting agent and does not inhibit RNA polymerase.
authors.affiliation: Department of Experimental Medicine, University of L'Aquila, Coppito-67100, L'Aquila, Italy.
authors.forename: Brunello
authors.initials: B
authors.lastname: Oliva
authors.forename: Alexander John
authors.initials: AJ
authors.lastname: O'Neill
authors.forename: Keith
authors.initials: K
authors.lastname: Miller
authors.forename: William
authors.initials: W
authors.lastname: Stubbings
authors.forename: Ian
authors.initials: I
authors.lastname: Chopra
mesh_terms: D000890:Anti-Infective Agents; D001426:Bacterial Proteins / Q000096:biosynthesis; D002462:Cell Membrane / Q000187:drug effects; D002991:Clofazimine / Q000494:pharmacology*; D003470:Culture Media; D004269:DNA, Bacterial / Q000096:biosynthesis; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D024881:Drug Resistance, Bacterial; D007917:Leprostatic Agents / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009391:Nephelometry and Turbidimetry; D011188:Potassium / Q000378:metabolism; D012329:RNA, Bacterial / Q000096:biosynthesis; D012293:Rifampin / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics
chemical_list: D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D003470:Culture Media; D004269:DNA, Bacterial; D007917:Leprostatic Agents; D012329:RNA, Bacterial; D002991:Clofazimine; D012321:DNA-Directed RNA Polymerases; C105078:RNA polymerase beta subunit; D011188:Potassium; D012293:Rifampin