Pathogenic Microorganisms 222 PHARM 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) is inGram Anythifterlayer lit aride Between outerand inner 1/3/2025 9  Gram positive and Gram negative Cell Wall Mommy 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 out.it feptedoglycon 1/3/2025 11 for Sachar lipopoly 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 from Lipopolysaccharide OM ❑Initiate innate immune response & activate macrophage to secrete cytokines: IL-1, TNF-a 1/3/2025 NEHE 17 2. PEPTIDOGLYCAN (PDG) All eubacteria possess PDG layer Surrounding the cytoplasmic membrane (CM) PDG is highly rigid structure in prevents osmotic lysis differentPress with 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 3rd AA is lysine or diaminopimelic (Di-amino acid) 4th AA is D-alanine 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 position & COOH of D-alanine in the 4th position of another chain Cross-linking occurs directly or by pentaglycine peptide 1/3/2025 19 9 January  it's a GIF Am d Biosynthesis of PDG PDOT bactorrendt peptidoglycan gates 1/3/2025 21  too Apr 8 Biosynthesis of PDG and Antibiotics That Act on PDG ❑All antibiotics that inhibit cell wall synthesis are bactericidal ❑NAG/NAM-pentapeptide Synthesis takes place in cytosol ❑Phosphoenolpyruvate (PFP)  NAM via transferase ✓Fosfomycin is an inhibitor of the MurA enzyme (UDP-N- acetylglucosamine-enolpyruvyltransferase) I ✓L-alanine  D-alanine via Alanine racemase reshii ❑2 D-alanine is converted to D-Alanyl D-Alanine via D-Ala D-Ala synthetase 1 ✓D-Cycloserine inhibits both enzymes so blocks ❑Bactoprenol transports NAG/NAM-P PDG ✓Bacitracin inhibits this transport Synthesis 1/3/2025 22 Biosynthesis of PDG and Antibiotics That Act on PDG Penicillin ❑Autolysins break β-(1-4) glyosidic bonds of PDG ❑NAG/NAM-P is inserted into the old PDG is considered as ❑Transglycosidase catalyzes formation of glyosidic bond e ❑This is the second step of biosynthesis of PDG B lactamase ✓Vancomycin inhibits Transglycosidase ❑Transpeptidase (PBP) reforms peptide cross-links between rows and layers of PDG to make a wall strong ❑This is the final step of biosynthesis of PDG ✓β-lactams inhibit Transpeptidase ✓Vancomycin binds to the D-Ala-D-Ala and prevents binding to PBP ✓Both prevent cross-linking 1/3/2025 23  in GramPositive Bacteria 3. TEICHOIC ACIDS (TA) ❑Associated with Gram positive bacteria ONLY ❑50% of the weight of the cell wall pÉÉ ❑Cell surface anionic glycopolymers ❑Responsible for negative charge ❑Highly immunogenic ❑Mediate adherence to mucosal cells 1/3/2025 24 3. TEICHOIC ACIDS (TA) ❑Two types of TAs A.WTAs divided into 2 components 1.Disaccharide unit (linkage unit): ❑N-acetylmannosamine & NAG-1-phosphate connected by β-(1,4)-glycosidic bond ❑NAG of Disaccharide unit is covalently linked to 6- OH of NAM in PDG 1/3/2025 25 TYPES OF TEICHOIC ACIDS (WALL- AND LIPO-TEICHOACIDS) 2. Main chain polymer: 18M a ❑ 40-60 unit of glycerol or ribitol joined via phosphodiester bond & carrying D-alanine, NAG or glucose substituent B.LTA is linked to cytoplasmic membrane with glycolipid anchor ❑glycolipid anchor is disaccharide unit of glucose connected by β- (1,6)-glycosidic bond with diacylglycerol ❑Function of WTA: Cell shape determination, cell division regulation, pathogenesis, antibiotic resistance ❑Function of LTA: Protection against cationic antimicrobial peptide 1/3/2025 26  IE 1/3/2025 27  Knowthe functions FUNCTIONS OF THE CELL WALL ❑Determining and Maintaining cell's shape ❑Countering the effects of osmotic pressure & prevent cell lysis ❑Providing attachment sites for bacteriophages ❑Providing a rigid platform for surface appendages- flagella, fimbriae & pili all originate from the wall and extend beyond it ❑Play an essential role in cell division ❑Site of major antigenic determinants of the cell surface ❑Resistance of Antibiotics H o k so far 1/3/2025 28  ATYPICAL CELL WALLS ❑Acid fast bacteria (Mycobacterium) mostlylipds ◦The cell envelop is more complex ◦High lipid content (40%) in its cell wall ◦Consists of >60% mycolic acid whereas the rest is PDG ◦Mycolic acid is long, branch chained fatty acids ◦Mycolic acid covalently binds to PDG via a polysaccharide ◦The complex lipids form a thick waxy layer outside PDG 1/3/2025 29  Cell wall of Mycobacterium 0,21 Branchings EI 1/3/2025 30  nocatwad Wall-less (CELL WALLS DEFICNIET) BACTERIA 1. Mycoplasmas (Pleuropneumonia-like organisms; PPLO) ❑ Lack CW entirely (not target for Antibiotics inhibit CW synthesis) ❑ Sterols in plasma membrane ❑ The smallest bacteria 150 nm 2. Archaea si PseudoPeptidoglycan ◦Wall-less or Walls of pseudomurein (lack NAM & D AAs) 3. L-forms ❑lose their cell wall during part of their life cycle ❑Can arise naturally by mutation in CW–encoding genes 1/3/2025 31 L-form: Defective cell wall bacteria membrane outer No a c for 1/3/2025 11th frame 32  I L-forms p's ❑L-form can induced artificially by; 1. Lysozyme digestion: it digests disaccharide in PDG 2. Penicillin treatment: it inhibits peptide bridges in PDG 3. When bacteria is placed in hypertonic solution ❑Two types of L-forms: 1.PROTOPLAST is a wall-less Gram-positive cell 8 2.SPHEROPLAST in Gram-ve lacking most of cell wall ❑More Stable than PROTOPLAST But if 1 ❑Can live & divide and/or return to its normal state mutinitiite ❑Forms cell wall again when penicillin or lysozyme is removed 33 ❑Both easily rupture in hypotonic solutions 1/3/2025 33  at 51.1 wholeregion 4. Periplasmic space (periplasm) ❑In gram negative only ❑Space between OM & CM ❑Keeps enzymes in this space ❑Contains PDG and gel-like solution of proteins ❑3 types of proteins 1.Biosynthetic e.g. Transglycosylases 2.Binding proteins: transport of specific molecules 3.Destroying or modifying of antibiotics ❑e.g. -lactamases or Degradative e.g. proteases 1/3/2025 34 5. PLASMA MEMBRANE ❑Cytoplasmic /inner membrane ❑Encloses the cytoplasm of a prokaryotic cell ❑Semi-permeable ❑Less rigid than eukaryotic plasma membrane ✓lack sterols except in: Asymmetric outermembrane ✓Mycoplasma ❑ Symmetric of phospholipids bilayer membrane ❑ Phospholipids bilayer with embedded proteins ❑ Protein-to-Phospholipid ratios are 3: 1 1/3/2025 35 1/3/2025 36 5. PLASMA MEMBRANE 1.Phospholipid bilayer (30-40%): each molecule contains ◦Polar head (hydrophilic) directed outward ◦composed of phosphate and glycerol ◦Non-Polar tail (hydrophobic) directed inward ◦composed of fatty acids 2. Proteins (60-70%): arranged in a variety of ways: ◦Peripheral proteins (lie at inner or outer leaflet) ◦Integral proteins ◦Transmembrane proteins 1/3/2025 37 MESOSOMES ❑Mesosomes are invaginations of CM that has a role in; ❑Cell wall formation during cell division ❑Site of Oxidative phosphorylation 1/3/2025 38  Functions of plasma membrane ✓Selective permeability (semipermeable) allows transport (passage) of some molecules ✓Provide carrier proteins and enzymes to synthesize and transport CW components and for metabolism n ✓Regulates cell division ✓Excretion of pathogenicity protein (IgA protease) ✓Site of respiration (Oxidative phosphorylation), Enzymes for ATP if production ✓Damage to CM by alcohols, quaternary ammonium compound, and polymyxin antibiotics causes leakage of cell contents 1/3/2025 39 Transport Across the Cell Membrane to low conc High ❑Basic rule: things spontaneously move from high concentration to low concentration (downhill). This process is called diffusion. ❑Getting many molecules into the cell is simply a matter of opening up a protein channel of the proper size and shape. ❑The molecules then move into the cell by diffusing down the concentration gradient. ❑Passive transport, or facilitated diffusion. 1/3/2025 40 Transport Across the Cell Membrane NoEnergy Energy Passive Active Property process process PD FD AT GT location Carrier mediated - + + + Conc. against - - + NA gradient Specificity - + + + Energy expended - - ATP PEP Solute modified - - - + during transport 1/3/2025 41  go out 1/3/2025 42 Antibiotics act on cell membrane ❑Polymyxins (AB and EE B) are positively charged ❑They forms an electrostatic interaction with the phosphate groups of a negatively charged lipid A on the outer membrane ❑Calcium and Magnesium ions are displaced from phosphates of the membrane lipids, destabilizing LPS, increasing membrane permeability, causing cytoplasmic leaking, and killing the cell ❑They can also bind and neutralize LPS released during bacterial lysis, preventing reactions to endotoxin Respiration processesinbacteria ❑A third activity of polymyxins is the inhibition of type II NADH oxidoreductases in the bacterial inner membrane, which are essential for respiration ❑Polymyxin is active against common Gram negative bacteria but not Gram negative cocci, Gram positive bacteria, or anaerobic bacteria 1/3/2025 43  12 January Thank You