All of the following are dimorphic fungi, except:

A. Histoplasma

B. Cryptococcus

C. Coccidioides

D. Blastomyces

E. Paracoccidioides

B. C.

Cryptococcus does not have a mold form, only yeast. Therefore, unlike Histoplasma, Coccidioides, Blastomyces, Paracoccidioides, and Sporothrix, it is not one of the

dimorphic yeasts. Other medically relevant fungi of the coccoid yeast-type, like Cryptococcus, include Torulopsis and Malassezia.

All of the following entities are in the differential diagnosis of a fuzzy colony on a plate, except:

A. hyaline septate mold

B. dematiaceous mold

C. dimorphic fungus

D. coccoid yeast

E. aseptate mold

D. coccoid yeast.

The presence of a fuzzy colony implies the presence of a mold. Based on that, one would not expect a coccoid yeast to be in the differential diagnosis. It is important to

also note that most dimorphic fungi will grossly appear as a mold by yeast conversion.

Which of the following media is most helpful in distinguishing the morphology of yeasts?

A. cottonseed agar

B. cornmeal agar with Tween 80

C. urea agar

D. brain-heart infusion medium

E. potato dextrose agar

B. cornmeal agar with Tween 80.

Cottonseed agar is used specifically to convert the mold phase of Blastomyces to the yeast form. Cornmeal with Tween 80 stimulates conidiation and chlamydospore

production, aiding in speciation. Urea agar is helpful in detecting urease which is produced by Cryptococcus neoformans. Brain-heart infusion is a non-selective medium

which will support the growth of saprophytic and pathogenic fungi. Potato dextrose agar is useful in demonstrating the production of pigment by Trichophyton rubrum.