Black dot ring worm is caused by –
**Core Concept**
The question is testing the student's knowledge of dermatophytes and their clinical presentations. **Dermatophytes** are a group of fungi that cause skin, hair, and nail infections, commonly known as ringworm. Black dot ringworm is a specific clinical manifestation of a dermatophyte infection.
**Why the Correct Answer is Right**
Black dot ringworm, also known as kerion celsi, is caused by **Trichophyton tonsurans**. This dermatophyte infects the hair shaft, leading to a condition characterized by the presence of black dots on the scalp, which are actually the remnants of infected hair. The infection causes inflammation and scarring, resulting in a kerion, a painful and swollen mass on the scalp.
**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because **Microsporum canis** is a common cause of ringworm in animals, but not typically associated with black dot ringworm in humans.
* **Option B:** Incorrect because **Epidermophyton floccosum** is a dermatophyte that causes skin and nail infections, but not typically associated with black dot ringworm.
* **Option C:** Incorrect because **Candida albicans** is a yeast that can cause skin infections, but not typically associated with black dot ringworm.
**Clinical Pearl / High-Yield Fact**
Black dot ringworm can be a challenging diagnosis, as it may mimic other scalp conditions, such as alopecia areata or tinea capitis. A thorough medical history, physical examination, and laboratory tests, including a fungal culture, may be necessary to confirm the diagnosis.
**Correct Answer: C. Trichophyton tonsurans**