Abstract
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 inMycobacterium smegmatisis enhanced both upon addition of both a proton motive force (pmf) uncoupler, carbonylcyanidem-chlorophenylhydrazone (CCCP), and upon addition ofortho-vanadate, an inhibitor of ATP-dependent efflux pumps. Both the Δψ and ΔpH 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 MDR1 P-glycoprotein, enhances INH accumulation in a manner similar too-vanadate. Verapamil, a calcium channel blocker, also enhances INH uptake. Taken together, the results provide evidence of the involvement of both pmf- and ATP-dependent extrusion systems in INH efflux inM. smegmatis,making it important to evaluate the role of such systems in INH resistance in pathogenic mycobacteria.
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