1. Bacterial Capsules @ Firm, gelatinous layer covering cell wall. @ Microcapsule detected by E.M. & serology @ Composed of water, saccharides & peptides @ Slime layer is common in capsulated bacteria growing on solid media (K. pneumoniae). @ Carbohydrates stimulate capsules @ Failure of production is due to starvation, & accumulation of enzymes.

3. Capsule Demonstration @ Negative staining by India ink. @ Serology of enterobacteria shows K-antigen (capsule) masking somatic antigen (cell wall). @ E.M. with difficulty due to shrinkage of microcapsule on drying. @ Capsule-swelling reaction is conducted by adding a specific antiserum to organism.

5. Functions of Capsules @ Protect bacteria against: bacteriophages, complement, antibiotics, phagocytes, lysozymes, colicines. @ Determine virulence of organism: Bacillus, Streptococcus, Yersinia, Haemophilus. @ Non-capsulated mutants of capsulated bacteria are found to be non-virulent.

7. Bacterial Cell Wall Functions: @ Gives the bacterial cell its shape & rigidity. @ Protects cell against high osmotic pressure and environmental imbalance @ Serves as antigenic determinant to cell. @ Contributes to virulence of organism.

9. @ Structure of gram positive cell wall is different from that of gram negative. Cell Wall of Gram Positive Bacteria @ Peptidoglycan found on surface & made of 16 square units & each unit is made of 4 subunits @ Peptidoglycan contains murein which forms the rigid elements of the wall. @ Peptidoglycan is found throughout the wall forming a complex matrix with teichoic acids.

11. Peptidoglycan Structure: @ Contains specific sugars as per each species: # Rhamnose: Found in streptococci. # Arabinose: Found in mycobacteria. @ It is resistant to complement and sensitive to lysozyme and lytic enzymes. @ It is composed of N-acetyl­glucosamine & N-acetylmuramic acid molecules linked together alternately in a chain by glycosidic bonds.

13. @ The carboxyl group of N-acetylmuramic acid is linked to a tetrapeptide chain containing L-alanine, D-isoglutamamide, L-lysine, and D-alanine. @ These tetrapeptides are joined together by covalent bond to make a chain. @ N-acetylmuramic acid molecules each carrying tetrapeptide side chains cross-linked together by peptide bridges.

15. Biosynthesis of Peptidoglycan: # In the cytoplasm a nucleotide is formed from UDP & five aminoacids: L-alanine, L-lysine, D-isoglutamamide, D-alanine and D-alanine. # The nucleotide is transferred from cytoplasm to cell membrane where it loses UDP and forms a complex with a lipid called bactoprenol.NAG & NAM are added to the nucleotide-bactoprenol complex. # This complex is transferred to cell wall where bactoprenol is liberated & the peptide subunit is cross-linked by covalent bonds, and terminal D-alanine is liberated.

17. Teichoic Acids @ There are two types of teichoic acids: * Glycerol-teichoic acid: in cell membrane * Ribitol teichoic acid: in cell wall. @ Cell wall teichoic acid is composed of a polymer of ribitol phosphate and N-acetyl- glucosamine. This polymer is joined to glycine molecule by ester bonds @ Teichoic acid is joined to the peptidoglycan in the cell wall by covalent bonds.

19. Functions of Teichoic Acids @ Bacterial antigenic determinant, used for serological identification of bacterial genera. @ Regulate action of reactions needed for cell growth and division. @ Binding of cell cations, e.g. Mg ++

21. Cell Wall of Gram Negative Bacteria * Peptidoglycan inner layer:10% of cell wt * Outer membrane layer containing: 1. Lipopolysaccharide that consists of: @12 sugars forming somatic O antigens. @Lipid A which acts as an endotoxin. 2. Lipoprotein links outer membrane layer with peptidoglycan inner layer by a covalent bond 3. Porins: acting as pores for passing small hydrophilic molecules 4. Proteins 5. phospholipids

23. @ The periplasmic space is found between theperiplasmic space peptidoglycan layer and the cell membrane. @ G-ve: No teichoic acids or lipoteichoic acids. @ G-ve: Have a convoluted surface structure. @ Lipopolysaccharide is responsible for : * Somatic (O) antigen * Endotoxic activity, bacteraemia, shock. * Leukopenia, hyperglycaemia * Impaired blood circulation