Susceptibility of M. tuberculosis growing in broth cultures and in human macrophages to MSO. (a) M. tuberculosis growing in broth cultures was incubated in the presence of various concentrations of MSO, and the numbers of CFU in the cultures were determined weekly for 6 weeks. Data are mean CFU per milliliter for triplicate cultures; the standard error (SE) was always ≤3%, except for one value of 6.1% (no MSO at 6 weeks). (b) Differentiated THP-1 cells, a human macrophage cell line, were infected with M. tuberculosis and incubated in the presence of various concentrations of MSO. The numbers of CFU in the cultures were determined on day 0 (3 h after infection), day 2, and day 5. Data are mean CFU per culture flask for triplicate cultures; all SEs were ≤2.4%.