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Chapter 15

Chapter 15. Microbial Mechanisms of Pathogenicity. Microbial Mechanisms of Pathogenicity. Pathogenicity The ability to cause disease Virulence The extent of pathogenicity. Portals of Entry. Mucous membranes Skin Parenteral route. Numbers of Invading Microbes.

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Chapter 15

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  1. Chapter 15 Microbial Mechanisms of Pathogenicity

  2. Microbial Mechanisms of Pathogenicity • Pathogenicity The ability to cause disease • Virulence The extent of pathogenicity

  3. Portals of Entry • Mucous membranes • Skin • Parenteral route

  4. 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

  5. Adherence • Adhesions/ligands bind to receptors on host cells • Glycocalyx Streptococcus mutans • Fimbriae Escherichia coli • M protein Streptococcus pyogenes • Opa protein Neisseria gonorrhoeae • Tapered end Treponema pallidum

  6. Penetration into the Host Cell Figure 15.2

  7. Enzymes • Coagulase Coagulate blood • Kinases Digest fibrin clots • Hyaluronidase Hydrolyses hyaluronic acid • Collagenase Hydrolyzes collagen • IgA proteases Destroy IgA antibodies • Siderophores Take iron from host iron- binding proteins • Antigenic variation Alter surface proteins

  8. Toxins • Toxin Substances that contribute to pathogenicity • Toxigenicity Ability to produce a toxin • Toxemia Presence of toxin the host's blood • Toxoid Inactivated toxin used in a vaccine • Antitoxin Antibodies against a specific toxin

  9. Exotoxin

  10. Exotoxins • A-B toxins or type III toxins Figure 15.5

  11. Exotoxins • Membrane-disrupting toxins or type II toxins • Lyse host’s cells by: • Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins) • Disrupting phospholipid bilayer

  12. Exotoxins • Superantigens or type I toxins • Cause an intense immune response due to release of cytokines from host cells • Fever, nausea, vomiting, diarrhea, shock, death

  13. Exotoxins Figure 15.4a

  14. Endotoxin Figure 15.4b

  15. Endotoxins Figure 15.6

  16. Cytopathic Effects of Viruses Table 15.4

  17. 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 • Ergot toxin • Claviceps

  18. Pathogenic Properties of Protozoa • Presence of protozoa • Protozoan waste products may cause symptoms • Avoid host defenses by • Growing in phagocytes • Antigenic variation

  19. Pathogenic Properties of Helminths • Use host tissue • Presence of parasite interferes with host function • Parasite's metabolic waste can cause symptoms

  20. Pathogenic Properties of Algae • Neurotoxins produced by dinoflagellates • Saxitoxin • Paralytic shellfish poisoning

  21. Portals of Exit • Respiratory tract • Coughing, sneezing • Gastrointestinal tract • Feces, saliva • Genitourinary tract • Urine, vaginal secretions • Skin • Blood • Biting arthropods, needles/syringes

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