**Question:** All of the following are examples of bactericidal drugs except -

A. Gentamicin
B. Vancomycin
C. Metronidazole
D. Penicillin G

**Correct Answer:** .

**Core Concept:**
Bactericidal drugs are medications that directly kill bacteria, while bacteriostatic drugs inhibit bacterial growth without killing the bacteria. Both types of drugs are essential for treating bacterial infections, depending on the type and severity of the infection. In this context, the correct answer to the question depends on understanding the pharmacological actions of each drug mentioned.

**Why the Correct Answer is Right:**
Gentamicin is a type of aminoglycoside antibiotic that exhibits bactericidal activity by interfering with protein synthesis in bacteria. It binds to the 30S ribosomal subunit, leading to the inhibition of translation and ultimately bacterial cell death. Therefore, Gentamicin is a correct example of a bactericidal drug.

Vancomycin is a glycopeptide antibiotic that acts as a bacteriostatic drug. It inhibits bacterial cell wall synthesis by binding to D-Ala-D-ala ligase, preventing the addition of D-Ala-D-Ala to the growing peptidoglycan chains in the bacterial cell wall.

Metronidazole is a nitroimidazole antibiotic primarily used against anaerobic bacteria, protozoa, and some anaerobic fungi. It acts as a bactericidal drug by generating reactive nitrogen and oxygen species that damage bacterial DNA, leading to cell death.

Penicillin G is a beta-lactam antibiotic that acts as a bacteriostatic drug. It inhibits bacterial cell wall synthesis by binding to the penicillin-binding proteins (PBPs), which are enzymes involved in peptidoglycan synthesis. This binding prevents the transpeptidation and transglycosylation reactions required for cell wall synthesis, ultimately inhibiting bacterial growth.

**Why Each Wrong Option is Incorrect:**
Option A (Penicillin G) is incorrect because it is a bacteriostatic drug, preventing bacterial growth without killing the bacteria.

Option B (Vancomycin) is incorrect as it functions as a bacteriostatic drug, inhibiting bacterial cell wall synthesis without causing cell death.

Option C (Metronidazole) is incorrect as it acts as a bactericidal drug, causing DNA damage and cell death.

Option D (Gentamicin) is incorrect because it is a bactericidal drug that interferes with protein synthesis, leading to bacterial cell death.

**Why the Correct Answer is Right:**
Penicillin G is a bacteriostatic drug that inhibits bacterial growth, preventing the cell wall synthesis. It does not directly kill the bacteria, making it a bacteriostatic agent.

**Why Each Wrong Option is Incorrect:**
Option A (Penicillin G) is incorrect because it is a bacteriostatic drug, preventing bacterial growth without killing the bacteria.

Option B (Vancomycin) is incorrect as it functions as a bacteriostatic drug, inhibiting bacterial cell wall synthesis without causing cell death.

Option C (Metronidazole) is