FIG. 3.

Standard rifampin-resistant (•; H₃₇Rv [ATCC 35838]) and rifampicin-sensitive (▪; H₃₇Ra [ATCC 35836]) M. tuberculosis strains were set up in culture and treated with rifampin (1 μg/ml) for 48 h before being processed for the MTT reduction assay. Rifampin at 1 μg/ml was able to completely inhibit MTT reduction by the rifampin-sensitive M. tuberculosis strain, while it did not affect the rifampin-resistant strain.