Question

1) Describe the five basic mechanisms of antibiotic action against bacterial cells. Give examples of drugs that are used in each category.

2) In many instances, resistance builds to antibiotics over time. Describe at least seven ways this resistance develops

Answer 1

Answer=

1.five basic mechanisms of antibiotic action against bacterial cells are as follows

1.Inhibition of cell wall synthesis -The cellular contents in bacteria are surrounded by an inner peptidoglycan cell wall in addition to an plasma membrane.Antibiotics that affect the structure of the cell wall act at different stages of peptidoglycan synthesis and cell wall construction.

examples- 1.Beta lactams - inhibition of peptidoglycan synthesis

2.Vancomycin - disrupts peptidoglycan cross linkage.

3.Bacitracin - disrupts movement of peptidoglycan precursors

2.Inhibition of protein synthesis -

examples -

30S Ribosome site

Aminoglycosides - Irreversibly bind 30 S ribosomal proteins.

Tetracyclines- block tRNA binding to 30S ribosome -mRNA complex.

50S ribosome site -

a.Chloramphenicol - binds peptidyl transferase component of 50S ribosome,blocking peptide elongation.(bacteriostatic)

b.Macrolides - Reversibly bind 50S ribosome,block peptide elongation.

c.Clindamycin - binds 50 S ribosome,blocks peptide elongation; inhibits peptidyl transferase by interfering with binding of amino acid-acyl-tRNA complex.

3.Alteration of cell membranes -

Examples-Polymyxins-cationic detergent like activity

Bacitracin - disrupt cytoplasmic membranes.

4.Inhibition of nucleic acid synthesis -

Examples -

DNA effects-Quinolones are group of antibiotics that specifically interfere with bacterial topoisomeraseII

Quinolones -inhibit DNA gyrases or topoisomerases required for supercoiling of DNA;bind to alpha subunit.

Metronidazole -metabolic cytotoxic byproducts disrupt DNA

RNA effects(Transcription)

Ripampicin -- binds to DNA-dependent RNA polymerase inhibiting initiation &

5.Antimetabolite activity -

Sulphonamide & Dapsone - compete with p-aminobenzoic acid preventing synthesis of folic acid.

Trimethoprim -inhibit dihydrofolate reductase preventing synthesis of folic acid.