Which antibiotic class is primarily associated with bactericidal activity by inhibiting cell wall synthesis, specifically by targeting penicillin-binding proteins?

• A. Aminoglycosides
• B. Macrolides
• C. Tetracyclines
• D. Beta-lactams

Answer: (D)

Understanding how antibiotics kill bacteria hinges on how they affect the bacterial cell wall. Beta-lactam antibiotics have a chemical structure that allows them to bind to penicillin-binding proteins, the enzymes responsible for cross-linking the peptidoglycan matrix that gives the bacterial cell wall its strength. By inhibiting these PBPs, beta-lactams prevent cross-linking, weakening the wall and causing the cell to rupture as it undergoes division. This makes them primarily bactericidal, since they actively lead to bacterial death during growth.

Other common classes work through different targets. Aminoglycosides disrupt protein synthesis by binding the 30S ribosomal subunit and causing misreading of mRNA. Macrolides block translocation on the 50S ribosomal subunit, often producing a bacteriostatic effect. Tetracyclines prevent the attachment of aminoacyl-tRNA to the ribosome, also typically bacteriostatic. While the first three classes affect other essential processes, only beta-lactams directly inhibit the enzymes that build and strengthen the cell wall, leading to bacterial death in actively growing bacteria.