Microbial Mechanisms of Pathogenicity

1. 15 Microbial Mechanisms of Pathogenicity

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

3. OVERVIEW

4. OVERVIEW

5. Portals of Entry or How Microbes Enter a Host • Mucous membranes • Skin • Parenteral route

6. Portals of Entry or How Microbes Enter a Host

7. Portals of Entry or How Microbes Enter a Host

8. 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.

9. Bacillus Anthracis

10. 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

11. Adherence

12. How Bacterial Pathogens Penetrate Host Defenses

13. How Bacterial Pathogens Penetrate Host Defenses • Capsule • Cell Wall Components – M protein, Opa, mycolic acid

14. Chemicals that Promote Bacterial Invasions • 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 • Invasins – cause ruffling of membrane and enhance penetration

15. Penetration into the Host Cell Figure 15.2

16. HOST CELL DAMAGE

17. ROBBING THE HOST CELL OF NUTRIENTS Takes it from: Hemoglobin, lactoferrin, Transferrin, and Ferritin Siderophore with Iron

18. DIRECT DAMAGE DIRECT DAMAGE OCCURS AS BACTERIAL CELLS MULTIPLY AND RUPTURE INFECTED CELLS.

19. 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 in a vaccine. • Antitoxin: Antibodies against a specific toxin.

20. DISEASES Table 15.4

21. Endotoxins Figure 15.4b

22. Exotoxin Figure 15.4a

23. Exotoxins • A-B toxins Figure 15.5

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

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

26. Exotoxins • Specific for a structure or function in host cell Figure 15.4a

27. Exotoxins

28. Endotoxins Figure 15.6

29. Cytopathic Effects of Viruses Table 15.4

30. 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

31. Pathogenic Properties of Fungi • Aflatoxin • Aspergillus • Mycotoxins • Neurotoxins: Phalloidin, amanitin • Amanita

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

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

34. Pathogenic Properties of Algae • Paralytic shellfish poisoning • Dinoflagellates • Domoic acid intoxication • Diatoms Figure 27.15

35. Figure 15.9 (5 of 5)

36. 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