The efficacies of common dyes in primary isolation media for recovery of pathogenic fungi.

Dyes incorporated into a basal medium of brain heart infusion, Sabhi, tryptic soy, or yeast extract--pepton--glucose (YxPG) agar for selective isolation of fungi were investigated. Dilutions of 1:500, 1:750, 1:1,000, 1:5,000, and 1:10,000 of 33 common dyes were tested against 11 gram-positive and 16 gram-negative bacteria. In addition, these dyes were tested against Cryptococcus neoformans, Candida albicans, and the dimorphic phases of Histoplasma capsulatum and Blastomyces dermatitidis. Twenty-one of the dyes did not inhibit any of the organisms tested. Brilliant green, gentian violet, and malachite green (at three dilutions) inhibited all the organisms tested. Methyl red was found to be the best dye in selecting for fungi. Several dyes were also found to inhibit selectively C. neoformans or C. albicans and the dimorphic fungi H. capsulatum or B. dermatitidis.