A narrow spectrum antibiotic is active against

Options

A. gram positive or gram negative bacteria
B. gram negative bacteria only
C. single organism or one disease.
D. both gram positive and gram negative bacteria.

Answer

### Step-by-Step Solution:

1. **Understanding Antibiotics**:
- Antibiotics are classified into two main categories: narrow-spectrum antibiotics and broad-spectrum antibiotics.

2. **Definition of Narrow-Spectrum Antibiotics**:
- Narrow-spectrum antibiotics are those that are effective against a limited range of bacteria. They specifically target either gram-positive or gram-negative bacteria, but not both.

3. **Examples of Narrow-Spectrum Antibiotics**:
- Some common examples of narrow-spectrum antibiotics include:
- **Penicillin**: Primarily effective against gram-positive bacteria.
- **Macrolides**: Effective against certain gram-positive bacteria and some gram-negative bacteria.
- **Vancomycin**: Primarily used against gram-positive bacteria.

4. **Application of Narrow-Spectrum Antibiotics**:
- These antibiotics are typically used to treat specific infections where the causative microorganism is known, minimizing the impact on normal flora in the body.

5. **Conclusion**:
- Therefore, a narrow-spectrum antibiotic is active against either gram-positive or gram-negative bacteria, depending on the specific antibiotic used.

### Final Answer:
A narrow-spectrum antibiotic is active against **either gram-positive or gram-negative bacteria**.

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