TABLE 4.

Growth rates of resistant mutants and susceptible M. tuberculosis in U937 macrophages

StrainMutationMIC (μg/ml)Doubling time (h)No. of divisionsRelative fitness
HarlingenNone (wild type)0.2546.03.61.00
Ser531→Trp (TCG→TGG)>32166.01.00.28 ± 0.06
His526→Tyr (CAC→TAC)>3272.92.40.63 ± 0.02
Ser522→Leu (TCG→TTG)>1691.31.90.50 ± 0.16
H37RaNone (wild type)0.25111.21.50.41 ± 0.12
H37RvNone (wild type)0.2550.63.30.91 ± 0.06
  • a Data shown represent the average of two to three independent replicate experiments for each of two independent isolates of the same mutant type. Standard errors for relative fitness are indicated. The doubling time was estimated from a plot of ln(visible cells) = f(time), where the slope is ln2/doubling time (hours). The relative fitness is the ratio of doubling time (wild type)/doubling time (mutant).