A man developed a pustule after striking by a thorn in the garden. Laboratory examination of the tissue specimen shows cigar-shaped budding yeasts. Most probable causative agent is:
First, I need to recall the organisms that present with pustules and have characteristic yeast morphology. Cigar-shaped budding yeasts make me think of certain fungal species. Common ones include Candida, but Candida usually has oval budding yeast. Then there's Histoplasma, which is a dimorphic fungus, but it's more associated with respiratory infections.
Wait, there's another fungus called Sporothrix schenckii. Sporotrichosis is a subcutaneous infection that can start with a pustule after a thorn prick or injury. The yeast form of Sporothrix is indeed described as cigar-shaped with a bud at one end. That fits the description here. So the likely answer is Sporothrix schenckii.
Now, checking the options. The question didn't list the options, but the correct answer is probably S. schenckii. Let me make sure about other possibilities. Cryptococcus has a capsule and is more for meningitis. Aspergillus is mold, not yeast. So the other options are not matching. The key here is the cigar-shaped budding yeast in a subcutaneous infection after a thorn injury. That's classic for sporotrichosis. So the correct answer is Sporothrix schenckii.
**Core Concept**
This question tests identification of fungal pathogens based on morphology and clinical presentation. *Sporothrix schenckii*, a dimorphic fungus, causes sporotrichosis, characterized by subcutaneous nodules/pustules after traumatic inoculation. Its yeast phase exhibits **cigar-shaped budding** in tissue, a hallmark diagnostic feature.
**Why the Correct Answer is Right**
*Sporothrix schenckii* is the causative agent of sporotrichosis, a cutaneous or subcutaneous fungal infection. After trauma (e.g., thorn prick), the organism transitions from its mold form in the environment to a **cigar-shaped yeast** in human tissue. This morphology is distinct from other yeasts like *Candida* (oval budding) or *Histoplasma* (small yeast cells in macrophages). The clinical context of a pustule and thorn injury further supports this diagnosis.
**Why Each Wrong Option is Incorrect**
**Option A:** *Cryptococcus neoformans* causes meningitis or pulmonary infections, not subcutaneous lesions. It has a **polysaccharide capsule** and is **not cigar-shaped**.
**Option B:** *Candida albicans* causes mucosal or systemic infections, with **oval budding yeasts** and pseudohyphae, not cigar-shaped forms.
**Option C:** *Aspergillus* is a mold causing invasive pulmonary or sinus infections, with **septate hyphae** in tissue, not yeast forms.
**Clinical Pearl / High-Yield Fact**
Remember **"Sporotrichosis = thorn prick + cigar yeast"**. Differentiate from *Histoplasma* (reticuloendothelial system, small yeast in macrophages) and *B