Antibiotics or antibacterials are a type of antimicrobial agents used specifically against bacteria and are often used in medical treatment of bacterial infections and certain parasitic infections.

Mechanism of Action: Antibacterial action generally falls within one of four mechanisms, three of which involve the inhibition or regulation of enzymes involved in

• cell wall biosynthesis,
• nucleic acid metabolism and repair, or
• protein synthesis, respectively.
• The fourth mechanism involves the disruption of membrane structure.

Inhibition of Cell Wall Synthesis

Vancomycin ---> Disrupts peptidoglycan cross-linkage

Bacitracin ---> Disrupts movement of peptidoglycan precursors (topical use)

Inhibition of Protein Synthesis (Translation)

Aminoglycosides ---> Irreversibly bind 30S ribosomal proteins (bactericidal)

Tetracyclines ---> Block tRNA binding to 30S ribosome-mRNA complex (b-static)

Chloramphenicol ---> Binds peptidyl transferase component of 50S ribosome, blocking peptide elongation (bacteriostatic)

Macrolides ---> Reversibly bind 50S ribosome, block peptide elongation (b-static)

Clindamycin ---> Binds 50S ribosome, blocks peptide elongation; Inhibits peptidyl transferase by interfering with binding of amino acid-acyl-tRNA complex

Inhibition of Nucleic Acid Synthesis

DNA Effects

Quinolones ---> Inhibit DNA gyrases or topoisomerases required for supercoiling of DNA; bind to alpha subunit

Metronidazole ---> Metabolic cytotoxic byproducts disrupt DNA

RNA Effects (Transcription)

Rifampin ---> Binds to DNA-dependent RNA polymerase inhibiting initiation & Rifabutin of RNA synthesis

Bacitracin (topical) ---> Inhibits RNA transcription

Antimetabolite Activity

Sulfonamides & Dapsone ---> Compete with p-aminobenzoic acid (PABA) preventing synthesis of folic acid

Trimethoprim ---> Inhibit dihydrofolate reductase preventing synthesis of folic acid

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