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Journal of Clinical Microbiology, May 1998, p. 1214-1219, Vol. 36, No. 5
Armauer Hansen Research Institute, Addis
Ababa, Ethiopia
Received 6 August 1997/Returned for modification 23 September
1997/Accepted 3 February 1998
We describe a test which uses the ability of viable cells to reduce
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) to
detect resistance to a bactericidal drug, rifampin, in in
vitro-cultured Mycobacterium tuberculosis. The assay shows a linear relationship between the number of viable bacteria and the
ability to reduce MTT. Dead mycobacteria were unable to reduce MTT.
Rifampin-sensitive M. bovis (BCG) and M. tuberculosis exposed to rifampin showed a rifampin
concentration-dependent inhibition of the ability to reduce MTT, while
the resistant strains were unaffected. The inhibition of MTT reduction
after treatment with rifampin paralleled the reduction in the number of
CFU. By using mixing experiments in which the population percentages of
rifampin-sensitive and -resistant strains were varied, the assay could
detect the presence of rifampin resistance in the mixture when at least
1% of the bacterial population was composed of drug-resistant strains. The assay is cheap, can be visually read, and requires less than 3 days
to obtain susceptibility results. The total time required to obtain
results, from the time sputum is received in the laboratory, is, in
most cases, less than 4 to 5 weeks, which is the time required for
primary culture of the bacteria. The MTT assay could, in combination with a test to detect resistance to isoniazid, be a cheap and rapid
screening method for multidrug-resistant M. tuberculosis that is affordable even by low-income countries where tuberculosis is a
major public health problem.
0095-1137/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Use of 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyl
Tetrazolium Bromide for Rapid Detection of Rifampin-Resistant
Mycobacterium tuberculosis

and
*
Corresponding author. Present address: Department of
Mycobacteriology, Statens Serum Institut, Artillerivej 5, DK-2300
Copenhagen S, Denmark. Phone: 45 3268 3720. Fax: 45 3268 3871. E-mail:
hmi{at}.ssi.dk.
Present address: Scientific, Technical and Research Commission,
Organization of African Unity (OAU), PMB 2359 Lagos, Nigeria.
Present address: Department of Mycobacteriology, Statens Serum
Institut, DK-2300 Copenhagen S, Denmark.
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