Early results from indirect drug susceptibility test for tubercle bacilli

The indirect susceptibility test results on L-J medium for tubercle bacilli against streptomycin, isoniazid and rifampicin were read at the end of 2 wk and compared with the results at 4 wk. It was found that drug resistance could be correctly predicted in over 70 per cent of cultures including multi-drug resistant tuberculosis (MDR TB) strains at the end of 2 wk. The susceptibility to para-nitrobenzoic acid (PNB) read at 2 wk was able to distinguish non-tuberculous mycobacteria from Mycobacterium tuberculosis cultures. The early detection of resistance by this procedure requires only minimum inputs, and can benefit the majority of patients harbouring drug resistant tubercle bacilli.