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Antimicrobial Agents and Chemotherapy, September 2009, p. 3675-3682, Vol. 53, No. 9
0066-4804/09/$08.00+0 doi:10.1128/AAC.00550-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Role of the Mycobacterium tuberculosis P55 Efflux Pump in Intrinsic Drug Resistance, Oxidative Stress Responses, and Growth
Santiago Ramón-García,1,2*
Carlos Martín,1
Charles J. Thompson,2,
and
José A. Aínsa1,
Departamento de Microbiología, Medicina Preventiva y Salud Pública, Universidad de Zaragoza, Zaragoza 50009, and CIBER Enfermedades Respiratorias, Spain,1 Department of Microbiology and Immunology, Life Sciences Centre, University of British Columbia, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada2
Received 23 April 2009/ Returned for modification 10 June 2009/ Accepted 18 June 2009
Bacterial efflux pumps have traditionally been studied as low-level drug resistance determinants. Recent insights have suggested that efflux systems are often involved with fundamental cellular physiological processes, suggesting that drug extrusion may be a secondary function. In Mycobacterium tuberculosis, little is known about the physiological or drug resistance roles of efflux pumps. Using Mycobacterium bovis BCG as a model system, we showed that deletion of the Rv1410c gene encoding the P55 efflux pump made the strain more susceptible to a range of toxic compounds, including rifampin (rifampicin) and clofazimine, which are first- and second-line antituberculosis drugs. The efflux pump inhibitors carbonyl cyanide m-chlorophenylhydrazone (CCCP) and valinomycin inhibited the P55-determined drug resistance, suggesting the active export of the compounds by use of the transmembrane proton and electrochemical gradients as sources of energy. In addition, the P55 efflux pump mutant was more susceptible to redox compounds and displayed increased intracellular redox potential, suggesting an essential role of the efflux pump in detoxification processes coupled to oxidative balance within the cell. Finally, cells that lacked the p55 gene displayed smaller colony sizes and had a growth defect in liquid culture. This, together with an increased susceptibility to the cell wall-targeting compounds bacitracin and vancomycin, suggested that P55 is needed for proper cell wall assembly and normal growth in vitro. Thus, P55 plays a fundamental role in oxidative stress responses and in vitro cell growth, in addition to contributing to intrinsic antibiotic resistance. Inhibitors of the P55 efflux pump could help to improve current treatments for tuberculosis.
* Corresponding author. Mailing address: Department of Microbiology and Immunology, Life Science Centre, University of British Columbia, 2350 Health Sciences Mall, Vancouver, British Columbia V6T 1Z3, Canada. Phone: (604) 822-8094. Fax: (604) 822-6041. E-mail: ramon{at}interchange.ubc.ca
Published ahead of print on 29 June 2009.
These authors contributed equally to this work.
Antimicrobial Agents and Chemotherapy, September 2009, p. 3675-3682, Vol. 53, No. 9
0066-4804/09/$08.00+0 doi:10.1128/AAC.00550-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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