Diagnostic medium containing inositol, urea, and caffeic acid for selective growth of Cryptococcus neoformans

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Abstract
An agar medium containing inositol and urea as sole carbon and nitrogen sources, caffeic acid and ferric citrate as agents for the selective pigmentation of Cryptococcus neoformans, gentamicin as a broad-spectrum bacterial antibiotic, and yeast nitrogen base without amino acids and ammonium sulfate (Difco) was tested against 137 clinical isolates, 4 survey specimens, and 11 ATCC yeast and yeast-like strains. All 28 strains of C. neoformans showed heavy growth and dark brown pigmentation after 36 h. All other tested species of Cryptococcus showed heavy growth after 36 h but only light brown pigmentation after 48 h. No growth was observed in any tested strains of Geotrichum, Pityrosporum, Rhodotorula, Saccharomyces, and Torulopsis. Only the Cryptococcus-like Candida humicola grew of the 8 species and 62 strains of Candida tested. Six of 15 strains of Trichosporon cutaneum and 1 of 2 strains of Trichosporon pullulans showed moderate growth after 48 h. Very different colonial and microscopic morphology and/or the absence of brown pigmentation easily differentiated these strains of T. cutaneum, T. pullulans, and C. humicola from C. neoformans. The growth- and pigmentation-providing characteristics of the medium were unaffected by 2 h of exposure to 254 nm of ultraviolet light.