<prompt> Mechanism of action of chloramphenicol is -Cell wall synthesis inhibitor50 S ribosome inhibitor30S ribosome inhibitorglycopeptidase inhibitor  <response>: Ans. is b i.e., SOS ribosome inhibitor The mechanism of action of antimicrobials can be divided into :1. Inhibition of cell wall synthesis Drugs inhibiting cell wall synthesis are : b-lactam antibiotics penicillin, cephalosporins, monobactoms, carbapenems, cyclosporine, bacitracin, vancomycin, fosfomycin. All antibiotic inhibiting cell wall synthesis are bactericidal.2. Inhibition of cell membrane function Drugs acting on cell membrane are polypeptides polymyxin, colistin, tyrothricin, polyenes amphotericin B, nystatin, hamycin, azoles ketoconazole, fluconazole, itraconazole. All antimicrobials that act on cell membrane are bactericidal.3. Inhibition of protein synthesis translation Drugs acting by inhibiting protein synthesis are tetracyclines, chloramphenicol, aminoglycosides, erythromycin, clindamycin, linazolide. All protein synthesis inhibitors are bacteriostatic except aminoglycosides and streptogramins which are bactericidal. These drugs can be divided into :a Based on the steps of translation protein synthesis on which drug act:i Freeze initiation : Aminoglycosides.ii Inhibit elongation : Tetracyclines, puromycin, chloramphenicol.iii Inhibit translocation : Clindamycin, erythromycin.iv Causing premature termination : Puromycin.b Based on ribosome on which they act:i 30 S ribosome: Tetracycline, streptomycin.ii 50 S ribosome : Chloramphenicol, erythromycin, clindamycin, Linezolid, pleuromutilins retapamulin.iii Both 30S and 50S ribosomes : Aminoglycosides except streptomycin.4. Interference with nucleic acid synthesis These drugs may be :1. Drugs directly affecting nucleic acids RNA or DNA DNA gyrase inhibitors - Quinolones nalidixic acid and fluoroquinolones and novobiocin. Drugs destroying DNA - Metronidazole, nitrofurantoin. Nucleotidenucleoside analogues - get incorporated into DNA or RNA and lead to formation of faulty nucleic acid that may be unstable or nonfunctional. Drugs are - Acyclovir, Zidovudin, Idoxuridine. DNA dependent RNA polymerase inhibitors - Rifampicin2. Drugs acting indrectly by affecting intermediary metabolism They either inhibits folate synthase sulfonamide, PAS, dapsone or dihydrofolate reductase Trimethoprim, pyrimethamine so that tetrahydrofolate can not be synthesized, which is essential for the synthesis of DNA. 