Sequence analysis of the drug-resistant rpoB gene in the Mycobacterium tuberculosis L-form among patients with pneumoconiosis complicated by tuberculosis

The aim of the present study was to investigate the mutational characteristics of the drug-resistant Mycobacterium tuberculosis L-form of the rpoB gene isolated from patients with pneumoconiosis complicated by tuberculosis, in order to reduce the occurrence of the drug resistance of patients and gain a more complete information on the resistance of the Mycobacterium tuberculosis L-form. A total of 42 clinically isolated strains of Mycobacterium tuberculosis L-form were collected, including 31 drug-resistant strains. The genomic DNA was extracted, then the target genes were amplified by polymerase chain reaction and the hot mutational regions of the rpoB gene were analyzed by direct sequencing. The results revealed that no rpoB gene mutation was present in 11 rifampicin (RFP)-sensitive strains, while conformational changes were identified in 31 RFP-resistant strains. The mutation rate was 93.55% (29/31) in the resistant strains, and was frequently concentrated in codons 531 (51.61%; 16/31) and 526 (32.26%; 10/31), mainly occurring by case substitutions, including 27 unit point mutations and two two-point mutations. The novel mutation identified in codon 516 had not been previously reported. The substitution of highly-conserved amino acids encoded by the rpoB gene resulted in the molecular mechanism responsible for RFP resistance in the Mycobacterium tuberculosis L-form. This also demonstrated that the rpoB gene is diversiform.