Rapid detection of mutations in rpoB gene of rifampicin resistant Mycobacterium tuberculosis strains by line probe assay

Background & objectives: Multidrug resistant (MDR) tuberculosis (TB) is a problem of increasing importance in the world due to limited treatment options. Resistance to rifampicin results from nucleotide changes in the gene encoding the 0 subunit of the RNA polymerase (rpoB) of Mycobacterium tuberculosis. Rifampicin resistance is considered as a marker for MDR TB. The nature and frequency of mutations in the rpoB gene of rifampicin resistant clinical isolates vary considerably according to the geographical location and very little information is available on specific mutational patterns in India. This study was undertaken to detect and characterize the rpoB gene mutation associated with rifampicin resistance in M. tuberculosis by line probe assay. Methods: A total of 36 strains of M. tuberculosis were analysed by INNO-LiPA Rif TB and compared with the results of conventional susceptibility testing method. After PCR amplification of the region of RNA polymerase involved in rifampicin resistance, the amplified product was hybridized with a set of 10 oligonucleotides immobilized onto a membrane strip. From the pattern obtained, the presence or absence of rifampicin resistance in the M. tuberculosis strains was assessed. Results: It was found that the M. tuberculosis probe was 100 per cent specific; the most frequently observed mutation was His-526-Tyr in the rpoB gene; and correlation between the results of the LiPA and those obtained by the classical susceptibility testing was excellent (100%). Interpretation & conclusion: INNO LiPA was found to be a reliable, simple, rapid and informative tool for the early detection and characterization of rpoB mutation associated with rifampicin resistance in M. tuberculosis in the clinical laboratory setting and may constitute an important molecular method for the control of tuberculosis.