Isoniazid accumulation in Mycobacterium smegmatis is modulated by proton motive force-driven and ATP-dependent extrusion systems

Resistance to isoniazid (INH), a frontline, antituberculosis drug, presents a major problem in the chemotherapy of tuberculosis. Although several targets of INH have been identified, the mechanism of INH resistance remains incompletely understood. This report demonstrates that INH accumulation in Mycobacterium smegmatis is enhanced both upon addition of both a proton motive force (pmf) uncoupler, carbonyl-cyanide m-chlorophenylhydrazone (CCCP), and upon addition of ortho-vanadate, an inhibitor of ATP-dependent efflux pumps. Both the Delta psi and Delta pH components of the pmf are likely to be involved as judged by the effects of valinomycin and nigericin, respectively, Reserpine, an inhibitor of the human MDRI P-glycoprotein, enhances INH accumulation in a man ner similar too-vanadate. Verapamil, a calcium channel blocker, so enhances INH uptake. Taken together, the results provide evidence of the involvement of both pmf- and ATP-dependent extrusion systems in INH efflux in M. smegmatis, making it important to evaluate the role of such systems in INH resistance ire pathogenic mycobacteria. (C) 1999 Academic Press.