Drug Susceptibility Testing of Mycobacterium Tuberculosis for Isoniazid and Rifampicin by Absolute Concentration and MTT method – A Comparative Study

Introduction: Tuberculosis has been a main cause of mortality andmorbidity globally. In spite of having anti-tuberculous drugs, eliminationof tuberculosis is difficult because of the drug resistance. In order toachieve vital therapy selection and prevention of resistance, expeditiousdetection along with drug susceptibility techniques are essential needsof the hour.Aim: To evaluate the MTT assay and the absolute concentration methodfor determining Mycobacterium tuberculosis susceptibility to rifampicinand isoniazidMethods: 71 isolates of Mycobacterium tuberculosis were tested forsusceptibility to the first-line medications isoniazid and rifampicin usingthe MTT assay and the absolute concentration method after sputumsamples that tested positive for acid-fast bacilli were gathered.Results: Of the 71 isolates, 14% (10) were resistant to isoniazid and9% (6) were resistant to rifampicin by absolute concentration method.Isoniazid resistance was seen in 13% (9) and 10% (7) were resistant torifampicin by MTT assay. Isoniazid mono resistance was observed in5 isolates and 1 isolate to rifampicin alone by absolute concentrationmethod. Two isolates that were mono-resistant to rifampicin and fourisolates that were mono-resistant to isoniazid were acquired using theMTT assay. Both the absolute concentration approach and the MTTexperiment revealed that 7% (5) of the isolates were multidrug resistant.Conclusion: Increasing numbers of resistant and multidrug-resistanttuberculosis (MDR-TB) strains have led to a daunting need for rapid,reliable, and accurate drug susceptibility testing. Hence, we concludedthat the absolute concentration method is better than the MTT assay interms of simplicity of performance though the results may be delayed. How to cite this article:Santharam P, Govindarajan V. Drug SusceptibilityTesting of Mycobacterium Tuberculosisfor Isoniazid and Rifampicin by AbsoluteConcentration and MTT method – A ComparativeStudy. J Commun Dis. 2025;57(1):85-90. DOI: https://doi.org/10.24321/0019.5138.202510