Esculin-based medium for isolation and identification of Cryptococcus neoformans

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Abstract
A simple medium was developed, using esculin as the substrate, for the isolation and identification of C. neoformans, C. neoformans produced a brown-black pigment on the medium; all other yeasts produced no pigment or were light yellow. Esculin is .beta.-glucose-6,7-dihydroxycoumarin. C. neoformans produced pigment because the 6,7-dihydroxycoumarin component of the esculin molecule was converted to a melanin-like pigment. The reaction was apparently similar to the conversion of diphenols, aminophenols and diaminobenzenes to melanin. Laboratory studies with isolates of C. neoformans, C. albidus, C. luteolus and C. terreus and representatives of the genera Candida, Torulopsis, Geotrichum and Rhodotorula, plus environmental field studies, demonstrated that over 95% of C. neoformans isolates were correctly identified, whereas all other fungi were excluded. Esculin agar was a sensitive, specific medium for the isolation and identification of C. neoformans. It was inexpensive and had a long storage life.