Drug-Susceptible Mycobacterium tuberculosis Beijing Genotype Does Not Develop Mutation-Conferred Resistance to Rifampin at an Elevated Rate

Open Access
Publisher Website
Google Scholar
Abstract
The Mycobacterium tuberculosis Beijing genotype has drawn attention because it is often strongly associated with multidrug-resistant tuberculosis (MDR-TB). A possible reason is that the Beijing strains may have an enhanced capacity to develop drug resistance. In this study, we used the Luria-Delbrück fluctuation test to investigate whether strains of Beijing and non-Beijing genotypes exhibit differences in the acquisition of drug resistance. The M. tuberculosis reference strain H37Rv and 12 fully drug-susceptible clinical isolates, 6 of which were of the Beijing genotype, were examined. To determine the distribution of rifampin-resistant mutants, 25 independent cultures were made for each strain. The average mutation frequencies for the non-Beijing (H37Rv included) and Beijing genotypes were estimated to be 4.4 × 10−8 and 3.6 × 10−8, respectively. The corresponding average mutation rates for the non-Beijing and Beijing strains were 1.3 × 10−8 and 1.1× 10−8 mutations per cell division, respectively. The results suggest that the association of the Beijing genotype with MDR-TB is not due to an altered ability to develop resistance.