1. Antibiotics and inhibition of cell wall in bacteria

2. The cell wall is a component of most microorganisms. All cell walls contain a rigid components. Several antibiotics are known to inhibit the biosynthesis of cell wall polymers in bacteria and fungi. Bacterial Cell wall

3. Composition and of cell wall Macromolecular components of cell wall: -Peptidoglycan -Lipopolysaccharides -Lipoproteins -Proteins -Polysaccharides

4. Peptidoglycan as heteropolymers 1- Aminopolysaccharides: - Alternative N- acetylglucosamine GLU-NAC and N-acetylmuramic acid Mur NAC 2- Amino acids: - L- alanine - D-glutamic - meso- diaminopimelic acid or L diaminopemilic acid - L- lysine - D-alanine

5. Gram negative bacteria

6. Gram positive bacteria

7. In gram +ve bacteria e.g Staphylococcus aureus all peptide chains are joined together through pentaglycin bridges and diaminopimelic acid is substituted by L- lysine.

8. Synthesis of cell wall

10. Penicillins In the presence of penicillins, bacterial cell undergoes a change to spherical form i.e it interferes with cell wall biosynthesis. Penicillin inhibits the last step inpeptidoglycan bisynthesis (i.e transpeptidation).

11. Mechanism of cell wall synthesis inhibition a- Penicillin may competitively inhibits transpeptidase. Inhibits transpeptidation by binding to the substrate at the free NH2 group of pentaglycin and preventing the formation of the peptide bond in the cross-linking reaction. (penicillin binds through its COOH group.

12. Antibiotics inhibiting bacterial cell wall This could be due to: a- Inhibition of one or more of the biosynthetic enzymes. Phosphonomycin, cycloserine and penicillin. b- Bind to the lipid carrier in the membrane e.g bacitracin. c-Complex with the growing point of peptidoglycans. e.g. Vanomycin

13. D- cycloserine is antagonist of D-alanine. If it present in media, bacteria transformed into spheroplasts. It inhibits the utilization of D-alanine in cell wall synthesis. But experimentally, bacterial growth could be restored by the addition of D-alanine. Cycloserine

14. Phosphonomycin It is a broad spectrum antibiotic. It inhibits the synthesis of cell wall through inhibiting the synthesis of MUR-NAC from UDP-Glc-NAC + PEP (Phosphoenolpyruvate).

15. http://www.microbelibrary.org/images/spenc er/spencer_cellwall.html Enjoy watching the animated lecture through this link