A Bacterium living as commensal in humans in colon (large intestine) and synthesizing vitamin Kand `B_12` there, is

Options

A. Vibrio cholerae
B. Bacillus anthracis
C. Escherichia coli
D. Entamoeba coli

Answer

To solve the question of identifying the bacterium that lives as a commensal in humans in the colon and synthesizes vitamins K and B12, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify a bacterium that is a commensal organism in the human colon and is responsible for synthesizing vitamins K and B12.

2. **Analyze the Options**: The options provided are:
- Vibrio cholerae
- Bacillus anthracis
- Escherichia coli
- Entamoeba coli

3. **Evaluate Each Option**:
- **Vibrio cholerae**: This is a gram-negative bacterium known for causing cholera, a serious disease. It is not a commensal organism in the human colon and is pathogenic in nature.
- **Bacillus anthracis**: This is a gram-positive bacterium that causes anthrax. It is also pathogenic and not a commensal organism in the human colon.
- **Escherichia coli**: This is a gram-negative, rod-shaped bacterium that is commonly found in the intestines of humans and other organisms. It is known to be a commensal organism in the human colon and plays a beneficial role by synthesizing vitamins K and B12.
- **Entamoeba coli**: This is a protozoan, not a bacterium, and while it is found in the gastrointestinal tract, it does not synthesize vitamins K and B12.

4. **Identify the Correct Answer**: Based on the analysis, Escherichia coli is the only organism that fits the criteria of being a commensal bacterium in the human colon that synthesizes vitamins K and B12.

5. **Final Conclusion**: The correct answer to the question is **Escherichia coli**.