Drug susceptibility testing of Mycobacterium leprae in the BACTEC 460 system

Abstract

The susceptibility of Mycobacterium leprae to clinical and experimental antileprosy agents was assessed in the BACTEC 460 system. Nude-mouse-derived M. leprae (10(7) cells), incubated in BACTEC 12B medium at 33 degrees C under reduced oxygen, maintained a fairly constant growth index (14CO2 evolution) for 2 to 3 weeks. At concentrations ranging from 0.031 to 2.0 micrograms/ml, dapsone, rifampin, clofazimine, ethionamide, ofloxacin, clarithromycin, and minocycline all effected reductions in the growth index within 1 to 2 weeks, the extent of inhibition increasing with the incubation time. An in vivo rifampin-resistant isolate displayed markedly reduced susceptibility to rifampin compared with an in vivo-susceptible strain. This system appears to be highly suitable for in vitro drug susceptibility testing of M. leprae.