How does penicillin inhibit enzymes in bacteria?

Penicillin functions as an antibiotic by targeting the structural integrity of replicating bacteria. Specifically, it inhibits the bacterial enzymes responsible for the synthesis of the cell wall.1

During the growth of a bacterium, the cell wall requires the cross-linking of strands of wall material to maintain its shape and protective function. Penicillin interferes with this process by inhibiting the enzymes that catalyze these cross-linking reactions. Furthermore, the drug activates other enzymes that actively break down the existing protective wall of the microorganism.21

Because human cells lack cell walls, they are not affected by this mechanism, making penicillin selectively toxic to bacteria. This process is only effective against microorganisms that are actively replicating and producing new cell walls. If bacteria develop resistance, they may produce an enzyme called β-lactamase (or penicillinase), which disrupts the internal structure of the penicillin molecule, thereby neutralizing its ability to inhibit the target enzymes.1