NADH Dehydrogenase Defects Confer Isoniazid Resistance and Conditional Lethality in Mycobacterium smegmatis |
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| Authors: | Lynn Miesel Torin R. Weisbrod Jovita A. Marcinkeviciene Robert Bittman William R. Jacobs Jr. |
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| Affiliation: | Department of Microbiology and Immunology1. and Department of Biochemistry,2. Howard Hughes Medical Institute, Albert Einstein College of Medicine, Bronx, New York 10461, and Department of Chemistry and Biochemistry, Queens College of the City University of New York, Flushing, New York 113673. |
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| Abstract: | Isoniazid (INH) is a highly effective drug used in the treatment and prophylaxis of Mycobacterium tuberculosis infections. Resistance to INH in clinical isolates has been correlated with mutations in the inhA, katG, and ahpC genes. In this report, we describe a new mechanism for INH resistance in Mycobacterium smegmatis. Mutations that reduce NADH dehydrogenase activity (Ndh; type II) cause multiple phenotypes, including (i) coresistance to INH and a related drug, ethionamide; (ii) thermosensitive lethality; and (iii) auxotrophy. These phenotypes are corrected by expression of one of two enzymes: NADH dehydrogenase and the NADH-dependent malate dehydrogenase of the M. tuberculosis complex. The genetic data presented here indicate that defects in NADH oxidation cause all of the mutant traits and that an increase in the NADH/NAD+ ratio confers INH resistance. |
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