A HIV positive female presents with an indurated ulcer over the tongue. Laboratory findings show growth in cornmeal agar at 20 degree celcius, microscopy showing hyphae and growth in human serum at 37 degree celcius show budding yeasts. The probable cause is –
## Core Concept
The question presents a case of a HIV-positive female with an indurated ulcer on the tongue, and laboratory findings that indicate a specific type of fungal infection. The key details are the growth characteristics of the organism at different temperatures and its microscopic morphology. This points towards a dimorphic fungus, which can exist as both hyphae and yeast forms under different conditions.
## Why the Correct Answer is Right
The organism in question grows as **hyphae** on cornmeal agar at 20°C (or room temperature), and as **budding yeasts** in human serum at 37°C (body temperature). This dimorphic characteristic is typical of certain pathogenic fungi. The description fits *Histoplasma capsulatum*, *Blastomyces dermatitidis*, *Coccidioides immitis*, and *Sporothrix schenckii*. However, *Sporothrix schenckii* is particularly known for causing skin ulcers (like the one described) through inoculation, and it grows as a mold at room temperature and as yeast at body temperature.
## Why Each Wrong Option is Incorrect
- **Option A:** Without the specific options provided, we can't directly address each, but we can infer based on common pathogens. For example, if *Candida* species were considered, they primarily exist as yeasts and don't typically show a dimorphic growth pattern as described.
- **Option B:** Similarly, without specifics, if another fungus doesn't exhibit the described temperature-dependent dimorphism, it would be incorrect.
- **Option D:** This would be incorrect for similar reasons as Option A and B, primarily if the organism doesn't match the described growth characteristics.
## Clinical Pearl / High-Yield Fact
A key point to remember is that *Sporothrix schenckii* infections are often associated with gardeners or individuals who work with soil or plants, as the fungus can enter the body through skin breaks. The classic presentation is a painless, indurated ulcer that may develop along lymphatic channels. In immunocompromised patients, like those with HIV/AIDS, the infection can disseminate.
## Correct Answer Line
**Correct Answer: C. Sporothrix schenckii**