Sporothrix schenckii infection follows a traumatic inoculation in a gardener who presents with a nodular lymphangitic pattern of lesions tracking up the arm. Laboratory diagnosis is best confirmed by:
- A Culture at 25°C showing white mold with conidia in a flower-like arrangement on slender conidiophores (floret pattern), confirming dimorphic nature at 37°C ✓
- B KOH preparation of pus showing thick-walled spherules with endospores
- C Serology — serum latex agglutination for Sporothrix antigen
- D Biopsy showing non-caseating granulomas with PAS-positive broad-based budding yeast
Correct answer: A. Culture at 25°C showing white mold with conidia in a flower-like arrangement on slender conidiophores (floret pattern), confirming dimorphic nature at 37°C
Explanation
Sporothrix schenckii is a dimorphic fungus. In the mold form (25°C), hyphae bear conidiophores with oval/pyriform conidia arranged in a daisy/flower-like (rosette) pattern — a highly characteristic microscopic morphology. At 37°C or in infected tissue, it converts to oval to cigar-shaped yeast cells. Culture on Sabouraud dextrose agar is the most sensitive diagnostic method; KOH of pus rarely shows organisms due to low fungal burden. The lymphocutaneous (sporotrichoid) pattern of spread is pathognomonic clinically.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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