A rapid and simple resazurin assay to detect minimum inhibitory concentrations of first-line drugs for Mycobacterium tuberculosis isolated from cerebrospinal fluid.

OBJECTIVES

Central nervous system tuberculosis (CNS-TB) is a devastating manifestation of TB. The most common form of CNS-TB is tuberculous meningitis. Drug-resistant TB poses a major threat to the control of TB worldwide. Timely treatment dramatically improves the outcome. Colorimetric techniques for drug susceptibility testing based on the oxidation-reduction principle give results quick and are less expensive. The objectives of this study were to compare the susceptibility of Mycobacterium tuberculosis isolated from cerebrospinal fluid to four first-line drugs using the MGIT automated mycobacterial detection system and the resazurin assay (RA) as well as to estimate the minimum inhibitory concentrations (MICs) by RA.

METHODS

A total of 42 M. tuberculosis isolates were analysed for their susceptibilities by MGIT and RA.

RESULTS

Of the 42 isolates, 35 gave concordant results with both methods. Agreement between the two tests for streptomycin and rifampicin was 100% with a Fleiss' kappa (κ) value of 1, whereas for isoniazid and ethambutol agreement was 92.86% and 90.48%, respectively, with κ values of 0.853 and 0.738.

CONCLUSION

The RA appears to be a good alternative to the automated MGIT technique in resource-limited settings.