Comparative in vitro activities of MDL 473, rifampin, and ansamycin against Mycobacterium intracellulare.

The susceptibilities of 20 clinical isolates of Mycobacterium intracellulare to rifampin, MDL 473, and ansamycin were determined by broth and agar dilution methods. Ansamycin was more active than MDL 473, which in turn was usually more active than rifampin by either method. The MICs for 90% of the strains tested by agar dilution were 1, 2, and 4 micrograms of ansamycin, MDL 473, and rifampin per ml, respectively.