Mechanisms of Action of Different Classes of Antibiotics

Antibiotics are potent drugs designed to treat bacterial infections by either killing bacteria or inhibiting their growth. They have revolutionized medicine and saved countless lives since their discovery. This article delves into the principal mechanisms of action of different classes of antibiotics currently in use.

Beta-lactam Antibiotics

Beta-lactam antibiotics, including penicillins, cephalosporins, carbapenems, and monobactams, are one of the most widely used classes of antibiotics. These drugs work by inhibiting bacterial cell wall synthesis. They do this by binding to enzymes called penicillin-binding proteins (PBPs), which are involved in the final steps of cell wall construction. This disruption weakens the cell wall and leads to osmotic lysis, effectively killing the bacteria.

Aminoglycosides

Aminoglycosides like gentamicin and streptomycin function by binding to the bacterial 30S ribosomal subunit. This binding interferes with protein synthesis by causing the misreading of mRNA, leading to the production of aberrant proteins that disrupt various cellular processes, ultimately resulting in bacterial death.

Tetracyclines

Tetracyclines also target the 30S ribosomal subunit but unlike aminoglycosides, they simply block the attachment of tRNA to the ribosome during protein synthesis. This prevents the addition of amino acids to the growing peptide chain, effectively halting protein synthesis and inhibiting bacterial growth.

Macrolides

Macrolides, such as erythromycin and azithromycin, act on the 50S subunit of the bacterial ribosome. They inhibit protein synthesis by preventing the translocation of the peptidyl-tRNA from the A-site to the P-site on the ribosome, thus inhibiting bacterial growth.

Fluoroquinolones

Fluoroquinolones, including ciprofloxacin and levofloxacin, target bacterial DNA gyrase and topoisomerase IV, enzymes necessary for DNA replication and transcription. By inhibiting these enzymes, fluoroquinolones prevent DNA replication and transcription, leading to rapid death of the bacteria.

Sulfonamides and Trimethoprim

Sulfonamides and trimethoprim are often used together to inhibit sequential steps in the bacterial synthesis of folic acid, a vitamin that bacteria need to produce DNA, RNA, and proteins. By inhibiting folic acid synthesis, these drugs prevent bacterial replication.