A COLORIMETRIC ASSAY FOR THE ENUMERATION OF CANDIDA-ALBICANS IN BIOLOGICAL SAMPLES AFTER AMPLIFICATION IN A SELECTIVE MEDIUM

The MTT (3 (4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide) colorimetric assay was redesigned to enumerate C. albicans in biologi cal samples. Major modifications include the total permeabilization of the Candida cells to the tetrazolium salt and the solubilization of t he intracellular purple-colored formozan for spectrophotometric analys is. A preliminary amplification of the Candida population to be quanti fied is carried out using a low pH antibiotic-containing synthetic sel ective medium. Growth curves are logarithmic and similar for 11 strain s of C. albicans. All strains grew in the blastospore phase whether in oculated as blastospores or hyphae. C. guillermondii and C. pseudotrop icalis also grow in this selective medium and give similar standard cu rves, 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. T he presence of indigenous bacteria, debris and host cells do not inter fere with Candida growth and enumeration. The sensitivity and the adap tability of the test make it a powerful tool in epidemiological and di agnostic studies as well as in vitro assays of Candida growth or growt h inhibition.