Study of the Rifampin Monoresistance Mechanism in Mycobacterium tuberculosis

Rifampin (RIF) susceptibility is a key factor in determining the treatment effectiveness of the standardized treatment regimens. InMycobacterium tuberculosis , both target gene mutation and the efflux pump play major roles in the resistance to antituberculosis drugs. By eliminating RIF-resistant strains withrpoB mutation, the choice of RIF-monoresistant strains may allow us to identify the RIF-specific efflux pump genes. This study explored the RIF monoresistance mechanism inM. tuberculosis . Data from DNA sequencing and MIC measurements revealed that specific mutations, including Ser531Leu and His526Asp in RpoB, show high-level drug resistance. Three-dimensional structure modeling provided further evidence that the affinity between RIF and RpoB mutants was in accordance with the drug resistance level of the corresponding isolates. Furthermore, transcription-level analysis among the nonmutated isolates indicated that three efflux pumps (Rv0783, Rv2936, and Rv0933) might be involved in exporting RIF from the cell. Compared to 8 μg/ml for wild-typeEscherichia coli , the MICs for the transgenicE. coli strains with either Rv0783 or Rv2936 were 32 and 16 μg/ml, respectively. In conclusion, our study indicated that several RpoB mutant types, including Ser531Leu and His526Asp, show high-level RIF resistance attributed to low affinity between RpoB mutant proteins and RIF. In addition, this work demonstrates that Rv2936 and Rv0783 may be responsible for low-level resistance to RIF by exporting RIF from cells. The predicted structure of RpoB and the newly identified efflux pumps in this study will provide a novel approach to design new drugs and develop novel diagnosis technologies.