Figure 2. Concentration- and time-dependent bactericidal effect of rifampin (RIF) toward low-density cultures of Mycobacterium tuberculosis BE-1585 (5.1 × 105 CFU/mL) (A) and M. tuberculosis EAI-1627 (6.8 × 105 CFU/mL) (B). Cultures were exposed to RIF at 2-fold increasing concentrations for 6 days at 37°C. After 1, 3, or 6 days of exposure, subcultures were performed on solid media to count CFUs. *Accurate CFU counting could not be performed because complete outgrowth of mycobacteria occurred on the sixth day of RIF exposure, leading to aggregation.