Biology – Antibiotics | e-Consult

Penicillin is an antibiotic that primarily targets bacteria by interfering with cell wall synthesis. Bacteria possess a rigid cell wall made of peptidoglycan, which provides structural support and protects the cell from osmotic pressure. This peptidoglycan layer is crucial for bacterial survival.

Penicillin's mechanism of action involves inhibiting the enzymes known as penicillin-binding proteins (PBPs). PBPs are responsible for cross-linking the peptidoglycan chains, which is essential for building a strong and stable cell wall. Penicillin structurally resembles the D-alanyl-D-alanine peptide sequence that is a substrate for these enzymes. It binds to the active site of PBPs, preventing them from carrying out their cross-linking function.

This inhibition weakens the cell wall, making the bacterial cell vulnerable to osmotic lysis. As water rushes into the cell due to the high solute concentration within, the weakened cell wall cannot withstand the pressure, leading to cell rupture and death. Penicillin is most effective against bacteria that are actively growing and synthesizing new cell walls.