Rapid in vitro metabolic screen for antileprosy compounds.

Measurement of intracellular ATP of Mycobacterium leprae after direct in vitro exposure to antimicrobial agents was evaluated as a rapid means of identifying potentially useful therapeutic agents. Nude mouse-derived M. leprae was incubated in an axenic modified Dubos medium in the presence or absence of antimicrobial agents for up to 3 weeks. ATP was then assayed by using the firefly bioluminescence technique. Rifampin, clofazimine, and ethionamide each effected a significantly accelerated rate of ATP decay compared with controls. Dapsone appeared inactive, possibly reflecting a general insensitivity of this system to compounds acting at certain loci. The system appeared suitable for assessing comparative activity of new structural analogs of clofazimine. Other active compounds included erythromycin, minocycline, chloramphenicol, gramicidin, and, to a lesser extent, cycloserine, cephalothin, ciprofloxacin, tetracycline, and gramicidin S. The penicillins, bacitracin, isoniazid, nalidixic acid, trimethoprim, polymyxin B, and griseofulvin were all inactive. The system appears sensitive to agents with various modes of action and may prove useful as a primary screen for antileprosy drugs.