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Appl Environ Microbiol. 1968 February; 16(2): 236-238
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Reduction of a Tetrazolium Salt in Determining Growth Activity of Yeast-Phase Histoplasma capsulatum

Departments of Microbiology and Tropical Public Health, Harvard School of Public Health, Boston, Massachusetts 02115

ABSTRACT

A colorimetric method using a tetrazolium compound, 3,4,5-dimethylthiozalil-(1 or 2),2,5-diphenyltetrazolium bromide (TTBr), was developed for studying the growth activity of yeast-phase Histoplasma capsulatum. Materials extracted in phosphate buffer, pH 7.0, from cells at different stages of growth reduced TTBr. Colorimetric changes were correlated with enzymatic activity. Under standardized conditions specified herein, the optical density of the reduced tetrazole was an index of the growth activity of the organism.