Microscopic Morphologic Features of the Yeast Forms of Various Dimorphic Fungi

The yeast form of Blastomyces dermatitidis is a large, 10-15 µm in diameter, thick-walled yeast cell that characteristically produces a single bud attached by a broad base.

Blastomyces dermatitidis yeast with single bud attached by a broad base

Blastomyces dermatitidis yeast with single bud attached by a broad base

Blastomyces Dermatitidis Yeast

Blastomyces Dermatitidis Yeast

Blastomyces

Blastomyces


Coccidioides immitis does not produce a yeast form in laboratory culture; rather, is identified in stained tissue sections by the production of varying sized spherules, ranging from 10 µm to over 100 µm in diameter. The larger, more mature spherules contain spherical endospores ranging from 2-4 µm in diameter.

Spherules of Coccidioides immitis are seen here in liver with H and E staining. Note the thick wall of the sperules containing endospores.

Spherules of Coccidioides immitis are seen here in liver with H and E staining. Note the thick wall of the sperules containing endospores.

Coccidioides immitis form round spherules about 20-35 mm in diameter and endospores are present in the mature form

Coccidioides immitis form round spherules about 20-35 mm in diameter and endospores are present in the mature form

Coccidioides immitis

Coccidioides immitis


Paracoccidioides brasiliensis also produces large yeast cells approximately the same size as those of Blastomyces dermatitidis, except multiple buds are attached by narrow necks, giving the appearance of a “mariner’s wheel“.

Paracoccidioides brasiliensis

Paracoccidioides brasiliensis

Paracoccidioides brasiliensis

Paracoccidioides brasiliensis


The yeast forms of Sporothrix schenckii are elongated cells that have been called “cigar bodies“.

yeast form of Sporothrix schenckii

yeast form of Sporothrix schenckii

tissue phase yeast of Sporothrix schenckii

tissue phase yeast of Sporothrix schenckii

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