Drug susceptibility of Mycobacterium tuberculosis Beijing genotype and association with MDR TB

Abstract

To determine differences in the ability of Mycobacterium tuberculosis strains to withstand antituberculosis drug treatment, we compared the activity of antituberculosis drugs against susceptible Beijing and East-African/Indian genotype M. tuberculosis strains. Beijing genotype strains showed high rates of mutation within a wide range of drug concentrations, possibly explaining this genotype's association with multidrug-resistant tuberculosis.

Figure 1

Frequency of rifampin (RIF)-resistant mutants in Mycobacterium tuberculosis Beijing and East-African/Indian (EAI) genotype strains (5 strains each) originating from Vietnam. Mutation frequencies were determined in duplicate. Statistical analysis was performed by using an unpaired Mann-Whitney test.

Figure 2

Concentration- and time-dependent bactericidal effect of rifampin (RIF) toward low-density cultures of Mycobacterium tuberculosis BE-1585 (5.1 × 10⁵ CFU/mL) (A) and M. tuberculosis EAI-1627 (6.8 × 10⁵ CFU/mL) (B). Cultures were exposed to RIF at 2-fold increasing concentrations for 6 days at 37°C. After 1, 3, or 6 days of exposure, subcultures were performed on solid media to count CFUs. *Accurate CFU counting could not be performed because complete outgrowth of mycobacteria occurred on the sixth day of RIF exposure, leading to aggregation.