Effects of clofazimine on potassium uptake by a Trk-deletion mutant of Mycobacterium tuberculosis.

OBJECTIVES

This study was designed to investigate the effects of the membrane-active, anti-mycobacterial agent, clofazimine, on potassium (K+)-uptake by a mutant of Mycobacterium tuberculosis (MTB), in which the Trk system, the major K+ transporter of this microbial pathogen, had been selectively inactivated.

METHODS

The ceoB and ceoC genes of MTB, which encode the TrkA proteins, CeoB and CeoC, were deleted by homologous recombination, and the double-knockout mutant and wild-type strains compared with respect to K+ uptake and growth in the presence and absence of clofazimine (0.015-2.5 mg/L) using radioassay procedures.

RESULTS

Surprisingly, the magnitudes of K+ uptake and rate of growth of the ceoBC-knockout mutant were significantly (P < 0.05) greater than those of the wild-type strain, due, presumably, to induction of a back-up transporter. Exposure of both the wild-type strain and ceoBC-knockout mutant of MTB to clofazimine was accompanied by dose-related decreases in K+ uptake, as well as growth, which were of comparable magnitude for both strains.

CONCLUSIONS

These observations demonstrate that the major K+ transporter of MTB, Trk, as well as an uncharacterized inducible back-up system, is equally sensitive to the inhibitory actions of clofazimine.