13. Patogenicity
Microbial Mechanisms of Pathogenicity Copyright © 2010 Pearson Education, Inc. Mechanisms of Pathogenicity Pathogenicity: The ability to cause disease Virulence: The extent of pathogenicity Copyright © 2010 Pearson Education, Inc. Portals of Entry Mucous membranes Skin Parenteral route Preferred portal of entry Copyright © 2010 Pearson Education, Inc. Numbers of Invading Microbes ID50: Infectious dose for 50% of the test population LD50: Lethal dose (of a toxin) for 50% of the test population Copyright © 2010 Pearson Education, Inc. Bacillus anthracis Portal of Entry Skin ID50 10–50 endospores Inhalation 10,000–20,000 endospores Ingestion 250,000–1,000,000 endospores Copyright © 2010 Pearson Education, Inc. Toxins Agent Botulinum Shiga toxin Staphylococcal enterotoxin Copyright © 2010 Pearson Education, Inc. ID50 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 Copyright © 2010 Pearson Education, Inc. Adherence Copyright © 2010 Pearson Education, Inc. Figure 15.1 Adherence Copyright © 2010 Pearson Education, Inc. Figure 15.1 Adherence Copyright © 2010 Pearson Education, Inc. Figure 15.1 Capsules Prevent phagocytosis Streptococcus pneumoniae Haemophilus influenzae Bacillus anthracis Copyright © 2010 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 Copyright © 2010 Pearson Education, Inc. Enzymes Coagulase: Coagulates fibrinogen Kinases: Digest fibrin clots Hyaluronidase: Hydrolyzes hyaluronic acid Collagenase: Hydrolyzes collagen IgA proteases: Destroy IgA antibodies Copyright © 2010 Pearson Education, Inc. Membrane Ruffling Copyright © 2010 Pearson Education, Inc. Figure 15.2 Antigenic Variation Alter surface proteins ANIMATION Virulence Factors: Hiding from Host Defenses Copyright © 2010 Pearson Education, Inc. Figure 22.16 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 Copyright © 2010 Pearson Education, Inc. Figure 15.2 Using the Host’s Nutrients: Siderophores Use host’s iron Copyright © 2010 Pearson Education, Inc. Figure 15.3 Direct Damage Disrupt host cell function Produce waste products Toxins ANIMATION Virulence Factors: Penetrating Host Tissues ANIMATION Virulence Factors: Enteric Pathogens Copyright © 2010 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 Copyright © 2010 Pearson Education, Inc. Exotoxins and Endotoxins Copyright © 2010 Pearson Education, Inc. Figure 15.4 Exotoxins Specific for a structure or function in host cell ANIMATION Virulence Factors: Exotoxins Copyright © 2010 Pearson Education, Inc. Figure 15.4a The Action of an A-B Exotoxin Copyright © 2010 Pearson Education, Inc. Figure 15.5 Membrane-Disrupting Toxins Lyse host’s cells by Making protein channels in the plasma membrane – Leukocidins – Hemolysins – Streptolysins Disrupting phospholipid bilayer Copyright © 2010 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 Copyright © 2010 Pearson Education, Inc. Exotoxin Source Relation to microbe Chemistry Mostly Gram + By-products of growing cell Protein Fever? No Neutralized by antitoxin? Yes LD50 Copyright © 2010 Pearson Education, Inc. Small Figure 15.4a Exotoxins & 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 + Copyright © 2010 Pearson Education, Inc. Endotoxins Source Relation to Microbe Chemistry Gram Outer membrane Lipid A Fever? Yes Neutralized by Antitoxin? No LD50 Copyright © 2010 Pearson Education, Inc. Relatively large Figure 15.4b Endotoxins and the Pyrogenic Response Copyright © 2010 Pearson Education, Inc. Figure 15.6 Cytopathic Effects of Viruses Copyright © 2010 Pearson Education, Inc. Figure 15.7 Cytopathic Effects of Viruses Copyright © 2010 Pearson Education, Inc. Figure 15.8 Pathogenic Properties of Fungi Fungal waste products may cause symptoms Chronic infections provoke an allergic response Tichothecene toxins inhibit protein synthesis Fusarium Proteases Candida, Trichophyton Capsule prevents phagocytosis Cryptococcus Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Fungi Ergot toxin Claviceps Aflatoxin Aspergillus Mycotoxins Neurotoxins: Phalloidin, amanitin Amanita Copyright © 2010 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 Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Helminths Use host tissue Presence of parasite interferes with host function Parasite's metabolic waste can cause symptoms Copyright © 2010 Pearson Education, Inc. Pathogenic Properties of Algae Paralytic shellfish poisoning Dinoflagellates Saxitoxin Copyright © 2010 Pearson Education, Inc. Figure 27.13 Portals of Exit Respiratory tract Coughing and sneezing Gastrointestinal tract Feces and saliva Genitourinary tract Urine and vaginal secretions Skin Blood Biting arthropods and needles or syringes Copyright © 2010 Pearson Education, Inc. Mechanisms of Pathogenicity Copyright © 2010 Pearson Education, Inc. Figure 15.9
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