Which class of antibiotics primarily inhibits bacterial cell wall synthesis by targeting PBPs?

• A. Macrolides.
• B. Fluoroquinolones.
• C. Beta-lactams (e.g., penicillins, cephalosporins).
• D. Tetracyclines.

Answer: (C)

Bacteria rely on a sturdy cell wall made of peptidoglycan, and penicillin-binding proteins carry out the final cross-linking that gives that wall its strength. Beta-lactam antibiotics mimic the normal substrate of these enzymes and bind to their active sites, irreversibly blocking transpeptidase activity. Without proper cross-linking, the wall weakens as the bacteria grow, and the cell bursts from osmotic pressure. Other major antibiotic classes don’t target the cell wall: macrolides inhibit protein synthesis by binding the 50S ribosome, fluoroquinolones disrupt DNA replication by inhibiting gyrase/topoisomerase, and tetracyclines block tRNA binding to the 30S ribosome. Because of this direct interference with cell wall construction, beta-lactams are the class that primarily inhibits bacterial cell wall synthesis by targeting PBPs.