Question

For each of the following, give its mechanism of action and whether it is cidal or static, and the organism that it has an effect on.

Sulfonamides                                                 

Penicillin

Cephalosporins                                              

Bacitracin

Streptomycin                    

Tetracycline

Answer 1

Sulfonamides - It is bacteriostatic. It acts as structural analog of p-aminobenzoic acid (PABA) and inhibit synthesis of folic acid. Folic acid is required for purine base formation.

Penicillin - It is bactericidal in nature and inhibits the peptidoglycan synthesis present in cell wall by binding to Penicillin binding proteins (PBPs). These proteins are located inside the bacterial cell wall and have transpeptidase and carboxypeptidase activity required for cross-linking of peptodoglycan. It also mediates cell lysis by inactivating inhibitor of autolytic enzymes known as autolysins.

Cephalosporins - It is a beta-lactam anitibiotic and bactericidal in nature. It binds irreversibly to transpeptidase which is required for cell wall formation by cross-linking peptidoglycans.

Bacitracin - It inhibits the synthesis of bacterial cell wall by preventing the transport of peptidoglycan precursors through the cytoplasmic membrane. It is bactericidal in nature.

Streptomycin - It is bactericidal antibiotic and irreversibly inhibits protein synthesis. It combines with 30S subunit of ribosome and interferes with formation of initiation complex. Also, it promotes incorporation of incorrect amino acid into the peptide, producing a non-functional proein.

Tetracycline - It is bacteriostatic in nature and binds to 30S subunit of ribosome and blocks the ribosomal A site. The aminoacyl tRNA molecules cannot bind to the A site and protein synthesis is inhibited.