Mutations in rpoB gene and their association with Rifampicin-resistance levels in clinical isolates of Mycobacterium tuberculosis

Present study was aimed to identify most frequent mutations in rpoB gene region and to evaluate the association between mutations in rpoB gene and resistance levels to Rifampicin in clinical isolates of Mycobacterium tuberculosis of different geographical regions of India. A total of 100 clinical isolates of Mycobacterium tuberculosis were included in this study. Drug susceptibility testing against first line anti-tuberculosis drugs was performed on LJ medium by conventional minimal inhibitory concentration (MIC) method and the mutation(s) in rpoB gene of M. tuberculosis isolates were analyzed by sequencing method. Of the 100 M. tuberculosis isolates, 31 (31.0%) and 18 (18.0%) were found resistant and susceptible for all four first-line anti-tuberculosis drugs. The genetic mutations were observed in 96% (72/75) rifampicin-resistant M. tuberculosis isolates, while 4% (3/75) of rifampicin-resistant isolates did not have any mutation in rpoB gene. The mutation TCG531TTG (Ser531Leu) was found as most common and frequent mutation in 69.3% (52/75) of rifampicin-resistant isolates of M. tuberculosis with MIC level (≥ 512mg/l). The mutation at codon 511 was associated with low degree (128mg/l) of rifampicin-resistance, deletions at codons 514-516 or substitution at codon 516 were found to be associated with moderate degree (256mg/l) of rifampicin-resistance and mutations at codon 526, 531 were associated with the high degree (512mg/l) of rifampicin-resistance in M. tuberculosis isolates of Indian origin. The findings of this study will be useful for the development of raid and more specific indigenous molecular tools for the early diagnosis of multidrug-resistant tuberculosis in the country.