Molecular characterisation of drug resistance in Mycobacterium tuberculosis isolates from North India

SETTING: A tertiary care hospital in North India. OBJECTIVES: To analyse the frequency of mutations associated with resistance to rifampicin (RMP), isoniazid (INH) and streptomycin (SM) in Mycobacterium tuberculosis. DESIGN: M. tuberculosis isolates from 171 pulmonary tuberculosis (TB) patients (newly diagnosed 102, 59.6%; retreated 69, 40.3%) were analysed. Drug susceptibility testing was performed using the proportion method and resistant isolates were characterised using the polymerase chain reaction, followed by restriction fragment length polymorphism and/or DNA sequencing, to screen for mutations in rpoB, katG, mabA-inhA and rpsL. RESULTS: Of the 171 isolates, 16.9% (29/171) were multidrug-resistant. Of the 102 newly diagnosed and 69 retreated cases, respectively 5.9% (6/102) and 33.3% (23/69) were multidrug-resistant. rpoB mutations were found in 100% (31/31) of the RMP-resistant isolates, the most common being S531L in 74.2% (23/31); katG315 mutations were found in 79.6% (35/44) of the INH-resistant isolates; however, no mabA-inhA (-15) mutation was found; rpsL mutations were found in 48.9% (24/49) of the SM-resistant isolates, and codon 43 mutation were found in 42.5% (21/49). CONCLUSIONS: This study characterises drug resistance-associated mutations in M. tuberculosis, information that could be used for the rapid screening of drug-resistant TB.