Skin scrapings from a patient with tinea corporis were taken and cultured on SDA. Figure shows the LCB mount. Likely identity of the causative dermatophyte is-
**Core Concept**
The question requires identification of a dermatophyte based on the characteristics observed under a microscope, specifically in the LCB (Lactophenol Cotton Blue) mount. Dermatophytes are a group of fungi that cause skin, hair, and nail infections in humans and animals. They are characterized by their ability to break down keratin, a protein found in skin, hair, and nails.
**Why the Correct Answer is Right**
The LCB mount is a diagnostic tool used to identify fungi, including dermatophytes. Microsporum gypseum is a type of dermatophyte that is commonly found in soil and can infect humans, causing tinea corporis (ringworm). In the LCB mount, M. gypseum is characterized by its brown to black pigmentation, and the presence of pigmented conidiophores and conidia. This distinctive appearance is a key diagnostic feature of M. gypseum.
**Why Each Wrong Option is Incorrect**
**Option A:** Epidermophyton floccosum is another type of dermatophyte, but it is typically white or light-colored in the LCB mount, and it does not have the characteristic pigmentation of M. gypseum.
**Option B:** Microsporum audouinii is a type of dermatophyte, but it is typically seen in children and causes a more severe form of tinea corporis. It is not typically associated with the pigmentation seen in the LCB mount.
**Option D:** Trichophyton rubrum is a common cause of tinea corporis, but it is typically white or light-colored in the LCB mount, and it does not have the characteristic pigmentation of M. gypseum.
**Clinical Pearl / High-Yield Fact**
It's worth noting that M. gypseum is often seen in individuals who have had contact with soil or have been exposed to animals, such as veterinarians or farm workers. This is because M. gypseum is commonly found in soil and can be transmitted to humans through skin-to-skin contact or through contact with contaminated soil or animal hair.
**Correct Answer Line**
✓ Correct Answer: C. Microsporum gypseum