Mechanism of Antibiotic Action

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Mechanism of Antibiotic Action

Mechanism of Antibiotic Action
The penicillins inhibit cell wall synthesis of bacteria. The mechanism is as follows: The cell wall of both Gram positive and Gram negative bacteria is composed of peptidoglycan and murein. Petptidoglycan is made up of polysaccharide chains containing alternating residues of N-acetylmuramic acid (M) and N-acetylglucosamine (G). Peptide units cross-link extending from the N-acetylmuramic acid and during bacterial wall synthesis these linkages are caused by precursors which are catalysed by specific enzymes (ex: transpepidases and carboxypeptidases).

These enzymes are regulatory proteins which bind to penicillin and hence are known as penicillin binding proteins (PBPs). When bacteria are exposed to penicillin, the antibiotic binds to the PBPs in the cell membrane followed by the release of autolytic enzymes that degrade the preformed cell wall and arrest further cell wall synthesis leading to death of bacteria.

The principal mode of action of tetracyclines is the inhibition of protein synthesis. The antibiotics bind to the 30S ribosomal sub-unit and prevent the attachment of aminoacyl-tRNA to be acceptor site on the messenger RNA (mRNA)-ribosome complex.

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