What is vancomycin's mechanism of action?

• A. Inhibits protein synthesis at 50S.
• B. Blocks DNA replication.
• C. Inhibits RNA polymerase.
• D. Prevents cell wall synthesis.

Answer: (D)

Vancomycin kills by preventing cell wall synthesis. It binds tightly to the D-Ala-D-Ala end of peptidoglycan precursors, blocking the enzymes that form cross-links in the wall. Without proper cross-linking, the cell wall weakens, water rushes in, and the bacterium bursts. This mechanism targets Gram-positive bacteria most effectively because their thick peptidoglycan layer is exposed to the drug.

Other pathways described correspond to different antibiotic classes: inhibiting protein synthesis at the 50S ribosome is how macrolides and related drugs work; blocking DNA replication is the action of fluoroquinolones; inhibiting RNA polymerase is what rifamycins do. Vancomycin’s action is specifically on the cell wall synthesis step.