The colonies seen growing on the bird seed agar appear smooth and have a distinct...

The colonies seen growing on the bird seed agar appear smooth and have a distinct reddish-brown pigmentation. The active ingredient in bird seed (Guizotia abyssinica) agar is caffeic acid, which is extracted and placed in an agar containing 1% glucose. Of the cryptococci, and other species of yeasts, Cryptococcus neoformans selectively produces the enzyme phenoloxidase, which oxidizes the caffeic acid in the medium to melanin, producing the red-brown pigmentation.

The other yeast species included in this exercise do not possess phenoloxidase activity and therefore remain non-pigmented when grown on bird seed agar.

The colonies shown in this photograph were grown on Guizotia abyssinica (bird seed) agar at 30°C for 72 hours. The most likely identification is: