FIG. 4.
Chromosomes of nonviable M. tuberculosis in mouse lungs are not removed or degraded rapidly. C57BL/6 mice were infected intravenously with M. tuberculosis (∼106 CFU per mouse). One group (A) received INH (25 mg kg−1 day−1) for 8 weeks starting at 4 weeks postinfection; a control group (B) was left untreated. At 4, 8, and 12 weeks postinfection, mice from INH-treated and untreated groups were sacrificed and lungs were removed. Viable counts (CFU) were quantified by plating serial dilutions of lung homogenates (open bars); total counts (CEQ) were quantified by QPCR (shaded bars). Bars represent mean CFU or CEQ values (n = 4 mice per group); error bars, standard deviations from the means. In pairwise comparisons of CFU values in the INH-treated group for 4 versus 8 weeks or 4 versus 12 weeks postinfection, differences were highly significant (P < 0.005). In pairwise comparisons of CEQ values in the INH-treated group for 4 versus 8 weeks or 4 versus 12 weeks postinfection, differences were not significant (P > 0.05). Results are representative of two experiments.