Pathogenic Microorganisms Lecture Notes PDF

Pathogenic Microorganisms 222 PHARM Bacterial structures and function 1/3/2025 2  Objectives ❑Provide details microscopic bacterial structure: ❑Internal Structure (Intracytoplasmic structure) ❑Bacterial cell wall Structure ❑Surface Structure (S...

Pathogenic Microorganisms 222 PHARM Bacterial structures and function 1/3/2025 2  Objectives ❑Provide details microscopic bacterial structure: ❑Internal Structure (Intracytoplasmic structure) ❑Bacterial cell wall Structure ❑Surface Structure (Structures outside cell wall) ❑Differentiate between Gram-positive & Gram-negative cell wall ❑Describe the bacterial movement ❑Describe the spore formation 1/3/2025 3  BACTERIAL STRUCTURE 1/3/2025 4  STRUCTURE OF EUBACTERIA II. Additional (non-essential) I. Essential structures Capsule Cell wall Slime layer Cell membrane Flagella Cytoplasm Pili, Fimbriae Ribosome Inclusions Nuclear material Spores Plasmids 1/3/2025 5  STRUCTURE OF EUBACTERIA I. External structure III. Internal structure II. Cell envelop (Extracytoplasmic) (Intracytoplasmic) Glycocalyx 1. Outer membrane Cytoplasm Flagella 2. Cell wall Ribosome Pili 3. Cell membrane Nuclear material Fimbriae Inclusions Spores Plasmids 1/3/2025 6 II. Cell Wall structures 1. Outer membrane (OM) 2. Peptidoglycan 3. Teichoic Acids 4. Periplasm 5. Cytoplasmic Membrane (CM) 1/3/2025 7 Cell Wall (CW) ❑The outer most component of bacteria external to cytoplasmic membrane ❑Highly rigid structure giving shape to the cell ❑Varies in thickness & chemical composition depend on bacterial type ❑Two types according to chemical composition of CW 1. Gram positive CW 2. Gram negative CW 1/3/2025 8  Cell Wall (CW) 1/3/2025 9  Gram positive and Gram negative Cell Wall Gram - cell wall Gram + cell wall Outer membrane Present (8 nm-thick) Absent Thin (7-8 nm) 2 layers Thick (20-80 nm) 40 layers Peptidoglycan (PDG) 5-10% of the cell wall 50% of the cell wall Periplasm Present Absent Teichoic acids Absent Present Mesosome Less prominent More prominent Flagella structure 4 rings in basal body 2 rings in basal body 1/3/2025 10 1. The outer Membrane (OM) ❑Present in Gram negative only ❑Outside of PDG ❑Asymmetric lipid bilayer i. Lipopolysaccharides (LPS) ii.Porin Proteins iii.Phospholipids iv.lipoproteins 1/3/2025 11 i. Lipopolysaccharides (LPS) ❑Hydrophilic- located in outer leaflet of OM ❑Confers negative charge to cell ❑LPS consists of; 1.Polysaccharides (Hydrophilic) ❑Extends into the cell exterior A.O-antigen (O-specific Polysaccharides) ❑Immunogenic e.g. E. coli O157:H7 ❑Up to 40 repeating units of 3-5 sugars ❑Highly varied among species 1/3/2025 13 i. Lipopolysachharides (LPS) B.Middle Core: ❑Oligosaccharide (five sugars) ❑Sugars [heptose and ketodeoxy-octonate (KDO)] ❑Attaches directly to lipid A through KDO ❑Similar in all Gram-negative bacteria 2.Lipid A (Hydrophobic): Endotoxin (pyrogen) ❑Composed of phosphorylated glucosamine disaccharide unit (β-1,6) ❑Decorated with multiple fatty acids that inserted in OM outer leaflet ❑Antigenic (PAMP) Initiates innate immune response 1/3/2025 14 ii. Porins proteins ❑Also called outer membrane proteins (Omp) ❑Form channels (pores) ❑located in both halves of OM PDG-associated proteins (OmpC & OmpF) ❑Responsible for passage of hydrophilic molecules e.g. sugars ❑Loss of porins  antibiotic resistance PDG-non-associated proteins (OmpA) ❑Provides receptor for some viruses and bacteriocins ❑Stabilizes mating cells during conjugation 1/3/2025 15 iii.Liporoteins (Braun) ❑Play role in stabilization of OM structure ❑Covalently bound to PDG layer ❑Anchoring inner leaflet of OM to PDG ❑Determine & maintain the shape of the bacteria iv.Phospholipids ❑Inner leaflet of OM resembles CM while outer leaflet contains LPS 1/3/2025 16  FUNCTIONS OF OM ❑Confers negative charge to cell ❑Maintains the bacterial structure ❑Provides protection from adverse conditions ❑OmpC & OmpF are Pores for entrance of hydrophilic molecules ❑OmpA provides receptor for some viruses; stabilizes mating cells during conjugation ❑Initiate innate immune response & activate macrophage to secrete cytokines: IL-1, TNF-a 1/3/2025 17 2. PEPTIDOGLYCAN (PDG) All eubacteria possess PDG layer Surrounding the cytoplasmic membrane (CM) PDG is highly rigid structure prevents osmotic lysis maintains the shape of bacteria Fully permeable to ions, amino acid, and sugars PDG layer is made up of ropelike linear polysaccharide chains cross- linked by short peptides Linear polysaccharide consists of repeating disaccharides of N- acetylglucosamine (NAG) & N-acetylmuramic acid (NAM) 1/3/2025 18 2. PEPTIDOGLYCAN (PDG) NAG and NAM connected by β-(1,4)-glyosidic bond Tetrapeptide is attached to NAM Usually composed of amino acids (AAs): L-Ala, D-Glu, L-Lys, D-Ala 1st & 2nd AA that attached to NAM may vary for different organisms 3 AA is lysine or diaminopimelic (Di-amino acid) rd 4 AA is D-alanine th Cross-linking of 2 different layers occurs between Tetrapeptides 3rd AA is critical for cross-linking of PDG chain Peptide cross-link is formed between NH2 of di-amino AA in 3rd th position & COOH of D-alanine in the 4 position of another chain Cross-linking occurs directly or by pentaglycine peptide 1/3/2025 19