Q.70 The antimicrobial activity of vancomycin is due to the ____________.
(A) inhibition of nucleic acid synthesis
(B) damage to the cytoplasmic membrane
(C) inhibition of cell wall synthesis
(D) regulation of DNA supercoiling
The antimicrobial activity of vancomycin primarily stems from its targeted inhibition of bacterial cell wall synthesis. This makes option (C) the correct answer for the question.
Option Analysis
Vancomycin binds to the D-Ala-D-Ala terminus of peptidoglycan precursors, preventing their incorporation into the cell wall and leading to bacterial lysis.
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(A) Inhibition of nucleic acid synthesis: Incorrect, as this mechanism applies to antibiotics like quinolones (e.g., ciprofloxacin targeting DNA gyrase) or rifampin (inhibiting RNA polymerase).
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(B) Damage to the cytoplasmic membrane: Incorrect; polymyxins or daptomycin disrupt membranes by altering potential and causing ion leakage, unlike vancomycin’s extracellular action.
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(C) Inhibition of cell wall synthesis: Correct; vancomycin specifically blocks peptidoglycan polymerization in Gram-positive bacteria, halting cross-linking.
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(D) Regulation of DNA supercoiling: Incorrect, as this involves topoisomerase inhibitors like novobiocin or quinolones, not glycopeptides.
Vancomycin stands as a cornerstone glycopeptide antibiotic, renowned for its antimicrobial activity of vancomycin against severe Gram-positive infections like MRSA. Its precision in targeting bacterial vulnerabilities makes it essential for exams like CSIR NET Life Sciences.
Mechanism of Vancomycin
Vancomycin exerts bactericidal effects by binding the D-Ala-D-Ala motif on peptidoglycan precursors (e.g., lipid II), blocking transglycosylation and transpeptidation. This halts cell wall assembly, triggers autolysins, and causes osmotic lysis in Gram-positive bacteria.
Why Not Other Options?
Nucleic acid inhibitors like rifampin block RNA polymerase, while membrane disruptors like daptomycin depolarize cells—neither matches vancomycin’s action. DNA supercoiling regulators (e.g., gyrase inhibitors) affect topology, irrelevant here.
| Mechanism | Example Antibiotics | Target Bacteria | Vancomycin Match? |
|---|---|---|---|
| Cell Wall Inhibition | Vancomycin, β-lactams | Gram-positive | Yes |
| Nucleic Acid Inhibition | Quinolones, Rifampin | Broad | No |
| Membrane Damage | Daptomycin, Polymyxins | Gram-positive/negative | No |
| DNA Supercoiling | Novobiocin | Gram-negative | No |
Clinical Relevance
Used IV for systemic infections or orally for C. difficile, vancomycin requires monitoring due to resistance risks like VRE. For CSIR NET aspirants, mastering this distinguishes it from other classes.
