Evaluation of 2,3,5–Triphenyl tetrazolium chloride (TTC) assay for drug susceptibility testing of M. tuberculosis

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Original Article

Author Details : Mangala Ghatole, Virendra Kashetty, Apeksha Ghule, Avinash Wuike

Volume : 4, Issue : 1, Year : 2017

Article Page : 99-103

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Abstract

Background: Control of tuberculosis is hampered by emergence of drug resistance such as MDR, XDR & TDR. Treatment of this disease will be facilitated if early reliable drug susceptibility profile is available. Various commercial systems are available but in resource poor country like India cheaper colorimetric methods are evaluated. One such method is using 2,3,5- Triphenyl tetrazolium chloride (TTC), which is an oxidation–reduction dye indicating cellular viability and growth. Colorimetric methods used in liquid media are shown to give better results than using them in Lowenstein–Jensen medium (LJ).
Material and Method: A total of 82 strains isolated from patients suffering pulmonary tuberculosis and identified as M. tuberculosis were subjected to DST for Isoniazid and Rifampicin by Indirect drug susceptibility testing using absolute concentration method. 1% TTC was incorporated in Middlebrook 7H9 broth along with the drugs and compared with drug containing LJ.
Results: Among the 82 strains, 9 (10.9%) strains were resistant to INH by both methods. Whereas 06 (7.3%) were resistant only in TTC. (sensitivity-100%, specificity -60%, positive predictive value- 91.8% and negative predictive value of 100%, P?0.0001). Similarly 11(13.4%) strains showed resistance to RMP by both methods, 08 (9.8%) were resistant by only TTC and 01 (1.2%) only by conventional method. (Sensitivity- 98.4%, specificity- 57.9%, PPV-88.6%, NPV-91.7%, P?0.0001).
Conclusion: Results were available for 60 (73.2%) and 70 (85.4%) of strains by TTC method for INH and RMP respectively in 07 days as against 28 days in conventional method.

Keywords: M. tuberculosis, Susceptibility Testing, TTC Assay

How to cite : Ghatole M, Kashetty V, Ghule A, Wuike A, Evaluation of 2,3,5–Triphenyl tetrazolium chloride (TTC) assay for drug susceptibility testing of M. tuberculosis. Indian J Microbiol Res 2017;4(1):99-103

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