Figure 4.

Mycobacterium bovis–bacille Calmette-Guérin (BCG) susceptibility to nicotinamide (NAM) and pyrazinamide (PZA) is restored in macrophages. A, Phorbol-12-myristate-13-acetate–differentiated U937 cells were infected with a M. bovis–BCG fluorescent reporter strain that expresses mCherry (BCG-mCherry). Cells were pretreated and then maintained with the indicated doses of each drug, and fluorescence was monitored. M.bovis-BCG lacks a functional nicotinamidase/pyrazinamidase (PncA) preventing the activation of prodrugs NAM and PZA. B, To confirm resistance to these drugs, replication of the BCG-mCherry reporter in 7H9 broth in the presence of each drug or rifampin (RIF; 0.1 μg/mL) was similarly measured based on daily fluorescence. Data are represented as means with standard deviations, as in Figure 1. *P < .05; †P < .001. Abbreviations: MIC₉₉, 99% minimum inhibitory concentration (replication in drug-free 7H9 medium using 1% of the experimental inoculum); NA, nicotinic acid; NS, not significant (P ≥ .05); RFUs, relative fluorescence units.