Which one is found in alimentary canal of humans ?

Options

A. Pseudomonas
B. Rhizobium
C. Bacillus
D. Escherichia coli.

Answer

To answer the question "Which one is found in the alimentary canal of humans?" we will analyze each of the given options step by step.

### Step 1: Analyze Pseudomonas
- **Description**: Pseudomonas is a genus of gram-negative bacteria.
- **Habitat**: It is commonly found in soil and moist environments.
- **Conclusion**: Since Pseudomonas is a potent human pathogen and not typically found in the human alimentary canal, it is an incorrect option.

### Step 2: Analyze Rhizobium
- **Description**: Rhizobium is a type of bacteria known for its nitrogen-fixing capabilities.
- **Habitat**: It is primarily found in the root nodules of leguminous plants, which are located in the soil.
- **Conclusion**: As Rhizobium is not found in the human alimentary canal but rather in soil, it is also an incorrect option.

### Step 3: Analyze Bacillus
- **Description**: Bacillus is a genus of bacteria that includes various species.
- **Habitat**: These bacteria are found in soil, water, and air.
- **Conclusion**: Many species of Bacillus are known human pathogens, and they do not typically reside in the human alimentary canal, making this option incorrect as well.

### Step 4: Analyze Escherichia coli (E. coli)
- **Description**: E. coli is a gram-negative bacterium.
- **Habitat**: It is commonly found in the intestines of humans and other warm-blooded organisms.
- **Role**: E. coli plays a crucial role in maintaining gut flora and is involved in the synthesis of vitamins such as B12 and K.
- **Conclusion**: Since E. coli is a normal inhabitant of the human alimentary canal and has a symbiotic relationship with humans, this option is correct.

### Final Answer:
The correct answer is **Escherichia coli (E. coli)**, as it is found in the alimentary canal of humans.

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