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

To solve the question regarding the activity of narrow spectrum antibiotics, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Antibiotics**:
- Antibiotics are classified based on their spectrum of activity against bacteria. They can be either narrow spectrum or broad spectrum.

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

3. **Classification of Bacteria**:
- Bacteria are classified into two main groups based on their cell wall structure:
- **Gram-positive bacteria**: These bacteria have a thick peptidoglycan layer and retain the crystal violet stain used in the Gram staining procedure.
- **Gram-negative bacteria**: These bacteria have a thinner peptidoglycan layer and do not retain the crystal violet stain, appearing pink after the Gram staining procedure.

4. **Options Analysis**:
- **Option A**: Gram positive or gram negative bacteria - This suggests a broad spectrum, which is incorrect for narrow spectrum antibiotics.
- **Option B**: Gram negative bacteria only - This aligns with the definition of narrow spectrum antibiotics, as they can target specific bacteria.
- **Option C**: Single organism or one disease - While narrow spectrum antibiotics can target specific organisms, this option is too vague.
- **Option D**: Both gram positive and gram negative bacteria - This describes broad spectrum antibiotics, not narrow spectrum.

5. **Conclusion**:
- Based on the definitions and classifications, the correct answer is **Option B: Gram negative bacteria only**.

### Final Answer:
A narrow spectrum antibiotic is active against **gram negative bacteria only**.

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