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

Abstract

Introduction: Tuberculosis has been a main cause of mortality and
morbidity globally. In spite of having anti-tuberculous drugs, elimination
of tuberculosis is difficult because of the drug resistance. In order to
achieve vital therapy selection and prevention of resistance, expeditious
detection along with drug susceptibility techniques are essential needs
of the hour.
Aim: To evaluate the MTT assay and the absolute concentration method
for determining Mycobacterium tuberculosis susceptibility to rifampicin
and isoniazid
Methods: 71 isolates of Mycobacterium tuberculosis were tested for
susceptibility to the first-line medications isoniazid and rifampicin using
the MTT assay and the absolute concentration method after sputum
samples that tested positive for acid-fast bacilli were gathered.
Results: Of the 71 isolates, 14% (10) were resistant to isoniazid and
9% (6) were resistant to rifampicin by absolute concentration method.
Isoniazid resistance was seen in 13% (9) and 10% (7) were resistant to
rifampicin by MTT assay. Isoniazid mono resistance was observed in
5 isolates and 1 isolate to rifampicin alone by absolute concentration
method. Two isolates that were mono-resistant to rifampicin and four
isolates that were mono-resistant to isoniazid were acquired using the
MTT assay. Both the absolute concentration approach and the MTT
experiment revealed that 7% (5) of the isolates were multidrug resistant.
Conclusion: Increasing numbers of resistant and multidrug-resistant
tuberculosis (MDR-TB) strains have led to a daunting need for rapid,
reliable, and accurate drug susceptibility testing. Hence, we concluded
that the absolute concentration method is better than the MTT assay in
terms of simplicity of performance though the results may be delayed.

How to cite this article:
Santharam P, Govindarajan V. Drug Susceptibility
Testing of Mycobacterium Tuberculosis
for Isoniazid and Rifampicin by Absolute
Concentration and MTT method – A Comparative
Study. J Commun Dis. 2025;57(1):85-90.

DOI: https://doi.org/10.24321/0019.5138.202510