| Mycobacterium tuberculosis (MTB), which is the pathogen of tuberculosis (TB), remains a major human public health problem throughout the world. According to the report from the World Health Organization, currently about one third of the world's population was infected by MTB and there is globally 9.15 million recorded cases of TB annually. The occurrence of resistance to drugs used to combat TB, particularly multi-drug resistant TB (MDR-TB), defined as resistance to at least isoniazid and rifampin (RIF), has become a significant public health problem in a number of countries and an obstacle to effective global TB control.;In this project, we firstly obtained high level RIF resistant Mycobacterium smegmatis (MSM) strains with obviously growth retardation by repeated drug selection. Comparative analysis of genomic sequences revealed 4 mutations in coding sequences, including two in rpoB (N484T and 1488F), one in MSMEG_0436 (V49M), and one in MSMEG_6872 (V181L). Characterization of these four mutations showed that the two mutations in rpoB were correlated to RIF resistance. The one in MSMEG_6872 can render obviously growth retardation when MSMEG_6872 is over-expressed. Interestingly, we found an MTB protein, Rvl367c, which has the same motif with MSMEG_6872, had an 1193V polymorphism in different MTB strains. The 193V variant was mainly found in Beijing/W or drug resistant non-Beijing/W family strains. The transformants, no matter MSMEG_6872 or Rvl367c, all exhibited slim and long rod shape compared to stocky and short rod appearance of the parental strain.;Mycobacterial cells must pay biological cost in order to obtain RIF resistance and survive in the high concentration of RIF. In our case, the growth arrest may be due to the mutation of MSMEG_6872 which disrupts the balance of cell wall elongation and cell division. |
