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Chapter 12: Microbial Pathogenicity

Chapter 12: Microbial Pathogenicity. Pathogenicity The ability to cause disease Virulence The extent of pathogenicity. Portals of Entry. Mucous membranes Skin Parenteral route. Numbers of Invading Microbes. ID 50 : Infectious dose for 50% of the test population

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Chapter 12: Microbial Pathogenicity

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  1. Chapter 12: Microbial Pathogenicity • Pathogenicity The ability to cause disease • Virulence The extent of pathogenicity

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

  3. 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

  4. Bacillus anthracis

  5. Adherence of Microbe • Adhesins/ligands bind to receptors on host cells • Glycocalyx Streptococcus mutans • Fimbriae Escherichia coli • Streptococcus pyogenes • Neisseria gonorrhoeae

  6. Pathogenicity Promoters • Coagulates blood • Digests fibrin clots • Hyaluronidase Hydrolyzes hyaluronic acid • Collagenase Hydrolyzes collagen

  7. Pathogenicity Promoters • IgA proteases Destroy IgA antibodies • Siderophores Take iron from host iron- binding proteins • Alter surface proteins

  8. Penetration into the Host Cell Figure 15.2

  9. Toxins • Toxin Substances that contribute to pathogenicity • Toxigenicity Ability to produce a toxin • Toxemia Presence of toxin in the host's blood • Toxoid Inactivated toxin used as a vaccine • i.e. diptheria and tetanus toxoid • Antitoxin Antibodies against a specific toxin

  10. Endotoxin Figure 15.4b

  11. Endotoxin

  12. Endotoxins Figure 15.6

  13. Endotoxins

  14. Exotoxins Figure 15.4a

  15. Types of Exotoxins • Cause an intense immune response due to release of cytokines from host cells • Fever, nausea, vomiting, diarrhea, shock, death

  16. Types of Exotoxins • Membrane-disrupting toxins • Lyse host cells by: • Making protein channels in the plasma membrane (e.g., ) • Disrupting phospholipid bilayer • S. aureus and Streptococci

  17. Types of Exotoxins • A-B toxins • Disrupts internal cellular mechanisms; • Clostridium botulinum produces an A-B neurotoxin • Vibrio cholerae produces an A-B enterotoxin Figure 15.5

  18. Exotoxins

  19. Exotoxin

  20. Pathogenic Properties of Fungi • Fungal metabolic waste products may cause allergies • Proteases • Vaginal yeast infection • Capsule prevents phagocytosis • LINK • Can cause skin or nervous tissue disease • Found in soil and pigeon droppings

  21. Pathogenic Properties of Fungi • Aflatoxin; second link • Aspergillus flavus • Infrequently, contaminated peanut butter recalled • Neurotoxins • mushrooms • May be fatal if ingested • Ergot toxin • Claviceps purpurea

  22. Pathogenic Properties of Protozoa • Avoid host defenses by • Growing inside host cell • i.e. • Antigenic variation • Avoiding host immune system • campers: be careful what you drink!

  23. Pathogenic Properties of Helminths • Presence of parasite may interfere with host function • i.e. parasite clogs lymphatic vessels link • Pathogenic Properties of Algae • Neurotoxins produced by • - Paralytic shellfish poisoning

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

  25. Mechanisms of Pathogenicity

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