Bacterial Firm, gelatinous layer covering cell Microcapsule detected by E.M. & Composed of water, saccharides & Slime layer is common in capsulated bacteria growing on solid media (K. Carbohydrates stimulate Failure of production is due to starvation, & accumulation of enzymes.
Capsule Negative staining by India Serology of enterobacteria shows K-antigen (capsule) masking somatic antigen (cell E.M. with difficulty due to shrinkage of microcapsule on Capsule-swelling reaction is conducted by adding a specific antiserum to organism.
Functions of Protect bacteria against: bacteriophages, complement, antibiotics, phagocytes, lysozymes, Determine virulence of organism: Bacillus, Streptococcus, Yersinia, Non-capsulated mutants of capsulated bacteria are found to be non-virulent.
Bacterial Cell Wall Gives the bacterial cell its shape & Protects cell against high osmotic pressure and environmental Serves as antigenic determinant to Contributes to virulence of organism.
@ Structure of gram positive cell wall is different from that of gram negative. Cell Wall of Gram Positive Peptidoglycan found on surface & made of 16 square units & each unit is made of 4 Peptidoglycan contains murein which forms the rigid elements of the Peptidoglycan is found throughout the wall forming a complex matrix with teichoic acids.
Peptidoglycan Contains specific sugars as per each species: # Rhamnose: Found in streptococci. # Arabinose: Found in It is resistant to complement and sensitive to lysozyme and lytic It is composed of N-acetylglucosamine & N-acetylmuramic acid molecules linked together alternately in a chain by glycosidic bonds.
@ The carboxyl group of N-acetylmuramic acid is linked to a tetrapeptide chain containing L-alanine, D-isoglutamamide, L-lysine, and These tetrapeptides are joined together by covalent bond to make a N-acetylmuramic acid molecules each carrying tetrapeptide side chains cross-linked together by peptide bridges.
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.
Teichoic There are two types of teichoic acids: * Glycerol-teichoic acid: in cell membrane * Ribitol teichoic acid: in cell 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 Teichoic acid is joined to the peptidoglycan in the cell wall by covalent bonds.
Functions of Teichoic Bacterial antigenic determinant, used for serological identification of bacterial Regulate action of reactions needed for cell growth and Binding of cell cations, e.g. Mg ++
Cell Wall of Gram Negative Bacteria * Peptidoglycan inner layer:10% of cell wt * Outer membrane layer containing: 1. Lipopolysaccharide that consists sugars forming somatic O 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
@ The periplasmic space is found between theperiplasmic space peptidoglycan layer and the cell G-ve: No teichoic acids or lipoteichoic G-ve: Have a convoluted surface Lipopolysaccharide is responsible for : * Somatic (O) antigen * Endotoxic activity, bacteraemia, shock. * Leukopenia, hyperglycaemia * Impaired blood circulation