FIG. 2.

Effect of rifampin on the ability of M. bovis BCG to reduce MTT. BCG treated with various concentrations of rifampin for 48 or 72 h showed a drug dose-dependent inhibition of the ability to reduce MTT (A). This reduction in the ability of rifampin-treated bacilli to reduce MTT paralleled a reduction in the number of CFU when these bacilli were recultured (B). In both experiments, 5 × 10⁷ bacilli were set up in culture, treated for 48 or 72 h with rifampin, and processed for the MTT or CFU assay as described in Materials and Methods.