Lung tuberculosis is caused by

Options

A. Pseudomonas aeruginosa
B. Mycobacterium tuberculosis
C. Streptococcus pneumoniae
D. Escherichia coli

Answer

### Step-by-Step Solution:

1. **Understanding Tuberculosis**: Begin by defining what tuberculosis (TB) is. Tuberculosis is an infectious disease primarily affecting the lungs, but it can also impact other parts of the body. It is caused by bacteria.

2. **Identifying the Causative Agent**: The specific bacterium responsible for causing lung tuberculosis is **Mycobacterium tuberculosis**. This bacterium is known for its slow growth and ability to survive in harsh conditions.

3. **Transmission of Tuberculosis**: TB spreads through the air when a person with active TB coughs or sneezes, releasing droplets that contain the bacteria. These droplets can be inhaled by others, leading to infection.

4. **Analyzing the Options**:
- **Pseudomonas aeruginosa**: This bacterium is associated with urinary tract infections and respiratory infections but is not the cause of tuberculosis.
- **Mycobacterium tuberculosis**: This is the correct answer as it is the specific bacterium that causes lung tuberculosis.
- **Streptococcus pneumoniae**: This bacterium is known for causing pneumonia and other respiratory infections but is not responsible for tuberculosis.
- **Escherichia coli**: Commonly found in the intestines, this bacterium is not related to tuberculosis.

5. **Conclusion**: Based on the analysis of the options, the correct answer to the question "Lung tuberculosis is caused by" is **Mycobacterium tuberculosis**.

### Final Answer:
Lung tuberculosis is caused by **Mycobacterium tuberculosis**.