Sporothrix schenckii infection (sporotrichosis) classically presents as a painless nodule at the site of thorn-prick injury that ulcerates and then develops a chain of similar nodules along the lymphatic drainage (lymphocutaneous sporotrichosis). Which morphological form of this dimorphic fungus is found in human tissues?

• A Broad-based budding yeast
• B Pseudohyphae with blastoconidia
• C Spherules containing endospores
• D Elongated cigar-shaped yeast ✓

Explanation

Sporothrix schenckii is a thermally dimorphic fungus that exists as branching hyphae with conidia at room temperature (in soil/on plants) but converts to elongated, oval 'cigar-shaped' yeast cells at 37°C in human tissue. Broad-based budding yeast is characteristic of Blastomyces dermatitidis. Pseudohyphae with blastoconidia are seen in Candida. Spherules containing endospores are pathognomonic of Coccidioides immitis.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

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