Chapter 15 Microbial Mechanisms of Pathogenicity 2013 Pearson
Chapter 15 Microbial Mechanisms of Pathogenicity © 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case
© 2013 Pearson Education, Inc.
Mechanisms of Pathogenicity § Pathogenicity: the ability to cause disease § Virulence: the extent of pathogenicity © 2013 Pearson Education, Inc.
Portals of Entry § § Mucous membranes Skin Parenteral route Preferred portal of entry © 2013 Pearson Education, Inc.
Numbers of Invading Microbes § ID 50: infectious dose for 50% of the test population § LD 50: lethal dose (of a toxin) for 50% of the test population © 2013 Pearson Education, Inc.
Bacillus anthracis Portal of Entry Skin ID 50 10– 50 endospores Inhalation 10, 000– 20, 000 endospores Ingestion 250, 000– 1, 000 endospores © 2013 Pearson Education, Inc.
Toxins Portal of Entry Botulinum Shiga toxin Staphylococcal enterotoxin © 2013 Pearson Education, Inc. ID 50 0. 03 ng/kg 250 ng/kg 1350 ng/kg
Adherence § Adhesins/ligands bind to receptors on host cells § Glycocalyx: Streptococcus mutans § Fimbriae: Escherichia coli § M protein: Streptococcus pyogenes § Form biofilms © 2013 Pearson Education, Inc.
Figure 15. 1 a Adherence. Adhesin (ligand) Pathogen Host cell surface Receptor Surface molecules on a pathogen, called adhesins or ligands, bind specifically to complementary surface receptors on cells of certain host tissues. © 2013 Pearson Education, Inc.
Figure 15. 1 b-c Adherence. E. coli bacteria (yellow-green) on human urinary bladder cells © 2013 Pearson Education, Inc. Bacteria (purple) adhering to human skin
Capsules § Prevent phagocytosis § Streptococcus pneumoniae § Haemophilus influenzae § Bacillus anthracis © 2013 Pearson Education, Inc.
Cell Wall Components § M protein resists phagocytosis § Streptococcus pyogenes § Opa protein inhibits T helper cells § Neisseria gonorrhoeae § Mycolic acid (waxy lipid) resists digestion § Mycobacterium tuberculosis © 2013 Pearson Education, Inc.
Enzymes § § § Coagulase: coagulates fibrinogen Kinases: digest fibrin clots Hyaluronidase: hydrolyzes hyaluronic acid Collagenase: hydrolyzes collagen Ig. A proteases: destroy Ig. A antibodies © 2013 Pearson Education, Inc.
Chapter 15, unnumbered figure A, p. 434. Blocked coronary artery © 2013 Pearson Education, Inc.
Chapter 15, unnumbered figure B, p. 434. © 2013 Pearson Education, Inc. Necrotizing fasciitis
Chapter 15, unnumbered figure C, p. 434. Mechanism of streptokinase Streptokinase Plasminogen Blood clot Plasmin Fibrin breakdown © 2013 Pearson Education, Inc.
Figure 15. 2 Salmonella entering intestinal epithelial cells as a result of ruffling. Ruffling of host cell plasma membrane Salmonella typhimurium © 2013 Pearson Education, Inc.
Figure 22. 16 How trypanosomes evade the immune system. Clone B Clone C Relative number of trypanosomes Clone A 0 © 2013 Pearson Education, Inc. 1 2 Weeks after infection 3 4
Penetration into the Host Cell Cytoskeleton § Invasins § Salmonella alters host actin to enter a host cell § Use actin to move from one cell to the next § Listeria © 2013 Pearson Education, Inc.
Figure 21. 12 Cold sores, or fever blisters, caused by herpes simplex virus. © 2013 Pearson Education, Inc.
Figure 15. 3 Structure of enterobactin, one type of bacterial siderophore. © 2013 Pearson Education, Inc.
Direct Damage § Disrupt host cell function § Produce waste products § Toxins ANIMATION Virulence Factors: Penetrating Host Tissues ANIMATION Virulence Factors: Enteric Pathogens © 2013 Pearson Education, Inc.
The Production of Toxins § § § Toxin: substance that contributes to pathogenicity Toxigenicity: ability to produce a toxin Toxemia: presence of toxin in the host’s blood Toxoid: inactivated toxin used in a vaccine Antitoxin: antibodies against a specific toxin © 2013 Pearson Education, Inc.
Figure 15. 4 Mechanisms of Exotoxins and Endotoxins. exotoxins endotoxins Exotoxins are proteins produced inside pathogenic bacteria, most commonly grampositive bacteria, as part of their growth and metabolism. The exotoxins are then secreted into the surrounding medium during log phase. Endotoxins are the lipid portions of lipopolysaccharides (LPS) that are part of the outer membrane of the cell wall of gramnegative bacteria (lipid A; see Figure 4. 13 c). The endotoxins are liberated when the bacteria die and the cell wall breaks apart. Cell wall Exotoxin: toxic substances released outside the cell Clostridium botulinum, an example of a grampositive bacterium that produces exotoxins Salmonella typhimurium, an example of a gramnegative bacterium that produces endotoxins Endotoxins: toxins composed of lipids that are part of the cell membrane © 2013 Pearson Education, Inc.
Exotoxins § Specific for a structure or function in host cell ANIMATION Virulence Factors: Exotoxins © 2013 Pearson Education, Inc.
Figure 15. 5 The action of an A-B exotoxin. DNA Exotoxin m. RNA A (active) A B (binding) B 1 Bacterium produces and releases exotoxin. 2 B (binding) component of exotoxin attaches to host cell receptor. 3 A-B exotoxin enters host cell by receptormediated endocytosis. 4 A-B exotoxin enclosed in pinched-off portion of plasma membrane during pinocytosis. 5 A-B components of exotoxin separate. The A component alters cell function by inhibiting protein synthesis. The B component is released from the host cell. Exotoxin polypeptides Bacterium A B Receptor Plasma membrane Nucleus Cytoplasm Host cell A B B A Protein © 2013 Pearson Education, Inc.
Membrane-Disrupting Toxins § Lyse host’s cells by § Making protein channels in the plasma membrane – Leukocidins – Hemolysins – Streptolysins § Disrupting phospholipid bilayer © 2013 Pearson Education, Inc.
Superantigens § Cause an intense immune response due to release of cytokines from host cells § Symptoms: fever, nausea, vomiting, diarrhea, shock, and death © 2013 Pearson Education, Inc.
Exotoxin Source Relation to microbe Chemistry Mostly gram-positive By-products of growing cell Protein Fever? No Neutralized by antitoxin? Yes LD 50 © 2013 Pearson Education, Inc. Small
Exotoxins and Lysogenic Conversion Exotoxin Corynebacterium diphtheriae A-B toxin Lysogeny + Streptococcus pyogenes Membrane-disrupting erythrogenic toxin + Clostridium botulinum A-B toxin; neurotoxin + C. tetani A-B toxin; neurotoxin Vibrio cholerae A-B toxin; enterotoxin + Staphylococcus aureus Superantigen + © 2013 Pearson Education, Inc.
Endotoxins Source Relation to Microbe Chemistry Gram-negative Outer membrane Lipid A Fever? Yes Neutralized by Antitoxin? No LD 50 © 2013 Pearson Education, Inc. Relatively large
Figure 15. 6 Endotoxins and the pyrogenic response. Macrophage Nucleus Endotoxin Hypothalamus of brain Prostaglandin Cytokines Fever Blood vessel Vacuole Bacterium 1 A macrophage ingests a gram-negative bacterium. © 2013 Pearson Education, Inc. 2 The bacterium is degraded in a vacuole, releasing endotoxins that induce the macrophage to produce cytokines IL-1 and TNF-. 3 4 The cytokines are released into the bloodstream by the macrophages, through which they travel to the hypothalamus of the brain. Pituitary gland The cytokines induce the hypothalamus to produce prostaglandins, which reset the body’s “thermostat” to a higher temperature, producing fever.
LAL Assay § Limulus amebocyte lysate assay § Amebocyte lysis produces a clot § Endotoxin causes lysis ANIMATION Virulence Factors: Endotoxins © 2013 Pearson Education, Inc.
Figure 15. 7 Some cytopathic effects of viruses. Inclusion body Cytoplasmic mass Nuclei © 2013 Pearson Education, Inc.
Figure 15. 8 Transformed cells in culture. © 2013 Pearson Education, Inc.
Pathogenic Properties of Fungi § Fungal waste products may cause symptoms § Chronic infections provoke an allergic response § Trichothecene toxins inhibit protein synthesis § Fusarium § Proteases § Candida, Trichophyton § Capsule prevents phagocytosis § Cryptococcus © 2013 Pearson Education, Inc.
Pathogenic Properties of Fungi § Ergot toxin § Claviceps § Aflatoxin § Aspergillus § Mycotoxins § Neurotoxins: phalloidin, amanitin Amanita © 2013 Pearson Education, Inc.
Pathogenic Properties of Protozoa § Presence of protozoa § Protozoan waste products may cause symptoms § Avoid host defenses by § Growing in phagocytes § Antigenic variation © 2013 Pearson Education, Inc.
Pathogenic Properties of Helminths § Use host tissue § Presence of parasite interferes with host function § Parasite’s metabolic waste can cause symptoms © 2013 Pearson Education, Inc.
Pathogenic Properties of Algae § Paralytic shellfish poisoning § Dinoflagellates § Saxitoxin © 2013 Pearson Education, Inc.
Figure 27. 13 A red tide. © 2013 Pearson Education, Inc.
Portals of Exit § Respiratory tract § Coughing and sneezing § Gastrointestinal tract § Feces and saliva § Genitourinary tract § Urine and vaginal secretions § Skin § Blood § Arthropods that bite; needles or syringes © 2013 Pearson Education, Inc.
Figure 15. 9 Microbial Mechanisms of Pathogenicity. When the balance between host and microbe is tipped in favor of the microbe, an infection or disease results. Learning these mechanisms of microbial pathogenicity is fundamental to understanding how pathogens are able to overcome the host’s defenses. H 1 N 1 flu virus portals of entry Mucous membranes • Respiratory tract • Gastrointestinal tract • Genitourinary tract • Conjunctiva Skin Parenteral route Number of invading microbes penetration or evasion of host defenses Capsules Cell wall components Enzymes Antigenic variation Invasins Intracellular growth Adherence Mycobacterium intracellulare Clostridium tetani Micrographs are not shown to scale. © 2013 Pearson Education, Inc. damage to host cells Siderophores Direct damage Toxins • Exotoxins • Endotoxins Lysogenic conversion Cytopathic effects portals of exit Generally the same as the portals of entry for a given microbe: • Mucous membranes • Skin • Parenteral route
- Slides: 43