What is the classic tissue morphology of Blastomyces dermatitidis?

What is the classic tissue morphology of Blastomyces dermatitidis?

• A. Broad-based budding yeast
• B. Narrow-based budding yeast
• C. Intracellular yeasts within macrophages
• D. Septate hyphae with acute-angle branching

Answer: (A)

In tissue, Blastomyces dermatitidis appears as large yeast cells that reproduce by broad-based budding. The buds are wide at the base and remain attached to the mother cell, giving a thick-walled, round yeast with a distinctive broad neck. This broad-based budding is a hallmark that sets Blastomyces apart from other fungi seen in tissue. As a dimorphic fungus, its environmental form is a mold with septate hyphae and conidia, but in human tissue it takes on the yeast form with broad-based buds. Other morphologies—such as small intracellular yeasts within macrophages (seen with Histoplasma) or spherules with endospores (seen with Coccidioides), or hyphae with acute-angle branching (a mold form seen in several genera)—do not match the classic tissue appearance of Blastomyces.

In tissue, Blastomyces dermatitidis appears as large yeast cells that reproduce by broad-based budding. The buds are wide at the base and remain attached to the mother cell, giving a thick-walled, round yeast with a distinctive broad neck. This broad-based budding is a hallmark that sets Blastomyces apart from other fungi seen in tissue.

As a dimorphic fungus, its environmental form is a mold with septate hyphae and conidia, but in human tissue it takes on the yeast form with broad-based buds. Other morphologies—such as small intracellular yeasts within macrophages (seen with Histoplasma) or spherules with endospores (seen with Coccidioides), or hyphae with acute-angle branching (a mold form seen in several genera)—do not match the classic tissue appearance of Blastomyces.