A colorimetric assay for the enumeration of Candida albicans in biological samples after amplification in a selective medium

Abstract

The MTT (3 (4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide) colorimetric assay was redesigned to enumerate C. albicans in biological samples. Major modifications include the total permeabilization of the Candida cells to the tetrazolium salt and the solubilization of the intracellular purple-colored formozan for spectrophotometric analysis. A preliminary amplification of the Candida population to be quantified is carried out using a low pH antibiotic-containing synthetic selective medium. Growth curves are logarithmic and similar for 11 strains of C. albicans. All strains grew in the blastopore phase whether inoculated as blatospores or hyphae. C. guillermondii and C. pseudotropicalis also grow in this selective medium and give similar standard curves, whereas C. tropicalis, krusei, parapsilosis and glabrata cannot be amplified due to the presence of cycloheximide. The assay was used to enumerate Candida in aqueous mouth washes and in mucosal tissues. The presence of indigenous bacteria, debris and host cells do not interfere with Candida growth and enumeration. The sensitivity and the adaptability of the test make it a powerful tool in epidemiological and diagnostic studies as well as in vitro assays of Candida growth or growth inhibition.