Molecular characterization of drug-resistant Beijing family isolates of Mycobacterium tuberculosis from Tianjin, China.

OBJECTIVE Tuberculosis remains a severe public health issue, and the Beijing family of mycobacterium tuberculosis (M. tuberculosis) is widespread in East Asia, especially in some areas in China, like Beijing and Tianjin. This study aimed at determining the mutation patterns of drug-resistant Beijing strains of M. tuberculosis isolated from Tianjin, China. METHODS A total of 822 M. tuberculosis isolates were screened for drug resistance by an absolute concentration method and the genotype was identified by PCR. 169 drug-resistant isolates of the Beijing family were analyzed for the potential mutations in the rpoB, katG, inhA promoter region and in rpsL, rrs and embB genes, which are associated with resistance to rifampin (RFP), isoniazid (INH), streptomycin (SM) and ethambutol (EMB) respectively by PCR and DNA sequencing. RESULTS Fifty-eight out of 63 RFP-resistant isolates were found to carry the mutations within the 81-bp RFP resistance determining region (RRDR) of the rpoB gene and the most frequent mutations occurred at codon 531 (44.4%), 526 (28.6%), and 516 (7.9%) respectively. 16 mutation patterns affecting 12 different codons around the RRDR of rpoB were found. Of 116 INH-resistant isolates, 56 (48.3%) had the mutation of katG 315 (AGC-->ACC) (Ser-->Thr), 3 (2.6%) carried S315N (AGC-->AAC) and 27 (16.0%) had the mutation of inhA-15A-->T. 84 out of 122 SM-resistant isolates (68.9%) displayed mutations at the codons 43 or 88 with AAG-->AGG (Lys-->Arg) of the rpsL gene and 22 (18.0%) with the mutations at positions 513A-->C, 516C-->T or 905 A-->G in the rrs gene. Of 34 EMB-resistant isolates, 6 had mutation with M306V (ATG-->GTG), 3 with M306I (ATG-->ATT), 1 with M306I (ATG-->ATA), 1 with D328Y (GAT-->TAT), 1 with V348L (GTC-->CTC), and 1 with G406S (GGC-->AGC) in the embB gene. CONCLUSION These novel findings extended our understanding of resistance-related mutations in the Beijing strains of M. tuberculosis and may provide a scientific basis for development of new strategies for diagnosis and control of tuberculosis in China and other countries where Beijing strains are prevalent.