One of the following is not the causal organism for ringworm.

Options

A. Microsporum
B. Trichophyton
C. Epidermophyton
D. Macrosporum

Answer

To determine which organism is not a causal agent for ringworm, we need to analyze the options provided. The known causal organisms for ringworm include:

1. **Microsporum** - This fungus is responsible for various types of tinea infections, including athlete's foot and other skin infections.
2. **Trichophyton** - Another fungus that causes tinea infections, including nail and skin infections.
3. **Epidermophyton** - This fungus is also involved in causing ringworm and tinea infections.

Now, we need to identify the organism that is not associated with ringworm.

The question states that one of the following is not a causal organism for ringworm. Based on the information provided:

- **Microsporum**, **Trichophyton**, and **Epidermophyton** are all known to cause ringworm.
- **Macrosporum** is not mentioned as a causal organism for ringworm in the context provided.

Thus, the correct answer is **Macrosporum**.

### Step-by-Step Solution:
1. **Identify the Causal Organisms**: Recognize that ringworm is caused by certain fungi.
2. **List the Known Causal Organisms**: The known fungi that cause ringworm are Microsporum, Trichophyton, and Epidermophyton.
3. **Analyze the Options**: Compare the options given in the question to the known causal organisms.
4. **Determine the Incorrect Option**: Identify which organism is not listed among the known causal agents. In this case, it is Macrosporum.
5. **Conclude**: State that Macrosporum is not a causal organism for ringworm.