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RESEARCH ARTICLE

Confinement-Induced Drug-Tolerance in Mycobacteria Mediated by an Efflux Mechanism Brilliant B. Luthuli1, Georgiana E. Purdy2, Frederick K. Balagaddé1* 1 KwaZulu-Natal Research Institute for Tuberculosis and HIV, Nelson R. Mandela School of Medicine, University of KwaZulu-Natal, Durban, 4001, South Africa, 2 Dept. of Molecular Microbiology and Immunology, Oregon Health and Sciences University, 3181 S. W. Sam Jackson Park Rd., Mail Code L220, Portland, OR, 97239, United States of America * [email protected]

Abstract

OPEN ACCESS Citation: Luthuli BB, Purdy GE, Balagaddé FK (2015) Confinement-Induced Drug-Tolerance in Mycobacteria Mediated by an Efflux Mechanism. PLoS ONE 10(8): e0136231. doi:10.1371/journal. pone.0136231 Editor: Jérôme Nigou, Centre National de la Recherche Scientifique—Université de Toulouse, FRANCE Received: April 23, 2015 Accepted: July 30, 2015 Published: August 21, 2015 Copyright: © 2015 Luthuli et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by the Howard Hughes Medical Institute (http://www.hhmi.org/) and the University of KwaZulu-Natal College of Health Sciences. Competing Interests: The authors have declared that no competing interests exist.

Tuberculosis (TB) is the world’s deadliest curable disease, responsible for an estimated 1.5 million deaths annually. A considerable challenge in controlling this disease is the prolonged multidrug chemotherapy (6 to 9 months) required to overcome drug-tolerant mycobacteria that persist in human tissues, although the same drugs can sterilize genetically identical mycobacteria growing in axenic culture within days. An essential component of TB infection involves intracellular Mycobacterium tuberculosis bacteria that multiply within macrophages and are significantly more tolerant to antibiotics compared to extracellular mycobacteria. To investigate this aspect of human TB, we created a physical cell culture system that mimics confinement of replicating mycobacteria, such as in a macrophage during infection. Using this system, we uncovered an epigenetic drug-tolerance phenotype that appears when mycobacteria are cultured in space-confined bioreactors and disappears in larger volume growth contexts. Efflux mechanisms that are induced in space-confined growth environments contribute to this drug-tolerance phenotype. Therefore, macrophageinduced drug tolerance by mycobacteria may be an effect of confined growth among other macrophage-specific mechanisms.

Introduction Tuberculosis, caused by infection with Mycobacterium tuberculosis (Mtb) remains one of the world’s deadliest diseases, killing an estimated 1.5 million people annually [1]. Whereas drugsusceptible forms of the disease are in principle curable, the duration of treatment courses is at least 6 months and may last years [2]. Multidrug resistant TB (MDR-TB) and extensively drug resistant TB (XDR-TB) have poorer and less certain outcomes [2–4]. It is expected that shortened antituberculosis treatment regimens will improve patient adherence to treatment, and thereby foster better case management and disease control and minimize the risk of drug resistance [5, 6]. An interesting aspect of long-term chemotherapy in TB is that, whereas more than 95% of the tubercle bacilli population detectable in a patient’s sputum can be cleared in the first few days of treatment, prolonged treatment is required to eradicate the residual minority

PLOS ONE | DOI:10.1371/journal.pone.0136231 August 21, 2015

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Confinement-Induced Drug-Tolerance in Mycobacteria

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