Isoniazid and rifampin drug susceptibility testing: application of 2,3,5-triphenyl tetrazolium chloride assay and microscopic-observation drug-susceptibility assay directly on Ziehl-Neelsen smear positive sputum specimens.

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Isoniazid and rifampin drug susceptibility testing: application of 2,3,5-triphenyl tetrazolium chloride assay and microscopic-observation drug-susceptibility assay directly on Ziehl-Neelsen smear positive sputum specimens.

Braz J Infect Dis. 2015 Nov 27;

Authors: Shinu P, Singh V, Nair A

Abstract
The current study was aimed to evaluate the performance of direct 2,3,5-triphenyl tetrazolium chloride assay (direct TTC assay) and direct microscopic observation drug susceptibility assay (direct MODS assay) with indirect proportion method [(using Löwenstein-Jensen (LJ) media (Indirect LJ PM)] directly on Ziehl-Neelsen (ZN) smear positive sputum specimens.
METHODS: Direct AFB smear positive sputum specimens (n=264) were subjected to isoniazid (INH) and rifampicin (RIF) drug susceptibility testing by direct TTC assay, direct MODS assay, and the performances were compared with indirect LJ PM.
RESULTS: The direct TTC assay demonstrated an overall sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 99.2%, 82.4%, 99.2%, and 88.5%, respectively, for the detection of INH and RIF resistant MTB isolates when compared to indirect LJ PM method. Likewise, the overall sensitivity, specificity, PPV, and NPV of direct MODS assay were 98.8%, 82.4%, 99.2%, and 78.2%, respectively.
CONCLUSION: The direct TTC assay was found to be an economical alternative method for the rapid and accurate detection of INH and RIF resistance from direct AFB smear positive sputum specimens.

PMID: 26638012 [PubMed - as supplied by publisher]