JAC Advance Access originally published online on February 4, 2004
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Journal of Antimicrobial Chemotherapy (2004) 53, 435-440
© 2004 The British Society for Antimicrobial Chemotherapy
Anti-staphylococcal activity and mode of action of clofazimine
1 Department of Experimental Medicine, University of L’Aquila, Coppito-67100, L’Aquila, Italy; 2 Antimicrobial Research Centre and Division of Microbiology, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
Received 27 August 2003; returned 8 December 2003; revised 15 December 2003; accepted 16 December 2003
Objectives: 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.
Keywords: Staphylococcus aureus, mechanisms of antibiotic action, membrane-disrupting agent
* Corresponding author. Tel: +44-113-233-5604; Fax: +44-113-233-5638; E-mail: i.chopra{at}leeds.ac.uk
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