Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Microbial Mechanisms of Pathogenicity

6,093 views

Published on

Microbial Mechanisms of Pathogenicity

  1. 1. 15 Microbial Mechanisms of Pathogenicity
  2. 2. <ul><li>Pathogenicity: The ability to cause disease. </li></ul><ul><li>Virulence: The extent of pathogenicity. </li></ul>Microbial Mechanisms of Pathogenicity
  3. 3. Portals of Entry <ul><li>Mucous membranes </li></ul><ul><li>Skin </li></ul><ul><li>Parenteral route </li></ul>
  4. 4. Numbers of Invading Microbes <ul><li>ID 50 : Infectious dose for 50% of the test population. </li></ul><ul><li>LD 50 : Lethal dose (of a toxin) for 50% of the test population. </li></ul>
  5. 5. Bacillus Anthracis 250,000-1,000,000 endospores Ingestion 10,000-20,000 endospores Inhalation 10-50 endospores Skin ID 50 Portal of Entry
  6. 6. Adherence <ul><li>Adhesions/ligands bind to receptors on host cells </li></ul><ul><ul><li>Glycocalyx: Streptococcus mutans </li></ul></ul><ul><ul><li>Fimbriae: Escherichia coli </li></ul></ul><ul><ul><li>M protein: Streptococcus pyogenes </li></ul></ul><ul><ul><li>Opa protein: Neisseria gonorrhoeae </li></ul></ul><ul><ul><li>Tapered end: Treponema pallidum </li></ul></ul>
  7. 7. Enzymes <ul><ul><li>Coagulase: Coagulate blood </li></ul></ul><ul><ul><li>Kinases: Digest fibrin clots </li></ul></ul><ul><ul><li>Hyaluronidase: Hydrolyses hyaluronic acid </li></ul></ul><ul><ul><li>Collagenase: Hydrolyzes collagen </li></ul></ul><ul><ul><li>IgA proteases: Destroy IgA antibodies </li></ul></ul><ul><ul><li>Siderophores: Take iron from host iron-binding proteins </li></ul></ul><ul><ul><li>Antigenic variation: Alter surface proteins </li></ul></ul>
  8. 8. Penetration into the Host Cell Figure 15.2
  9. 9. Toxins <ul><li>Toxin: Substances that contribute to pathogenicity. </li></ul><ul><li>Toxigenicity: Ability to produce a toxin. </li></ul><ul><li>Toxemia: Presence of toxin in the host's blood. </li></ul><ul><li>Toxoid: Inactivated toxin used in a vaccine. </li></ul><ul><li>Antitoxin: Antibodies against a specific toxin. </li></ul>
  10. 10. Endotoxins Figure 15.4b Relatively large LD 50 : No Neutralized by antitoxin? Yes Fever? Lipid Chemistry: Present in LPS of outer membrane Relation to microbe: Gram – Source:
  11. 11. Exotoxin Figure 15.4a Small LD 50 : Yes Neutralized by antitoxin? No Fever? Protein Chemistry: By-products of growing cell Relation to microbe: Mostly Gram + Source:
  12. 12. Exotoxins <ul><li>A-B toxins </li></ul>Figure 15.5
  13. 13. Exotoxins <ul><li>Membrane-disrupting toxins </li></ul><ul><ul><li>Lyse host’s cells by </li></ul></ul><ul><ul><ul><li>Making protein channels in the plasma membrane (e.g., leukocidins, hemolysins). </li></ul></ul></ul><ul><ul><ul><li>Disrupting phospholipid bilayer. </li></ul></ul></ul>
  14. 14. Exotoxins <ul><li>Superantigens </li></ul><ul><ul><li>Cause an intense immune response due to release of cytokines from host cells. </li></ul></ul><ul><ul><li>Fever, nausea, vomiting, diarrhea, shock, and death. </li></ul></ul>
  15. 15. Exotoxins <ul><li>Specific for a structure or function in host cell </li></ul>Figure 15.4a
  16. 16. Exotoxins + Superantigen. Staphylococcus aureus + A-B toxin. Enterotoxin Vibrio cholerae A-B toxin. Neurotoxin C. tetani + A-B toxin. Neurotoxin Clostridium botulinum + Membrane-disrupting. Erythrogenic. Streptococcus pyogenes + A-B toxin. Inhibits protein synthesis. Corynebacterium diphtheriae Lysogenic conversion Exotoxin
  17. 17. Endotoxins Figure 15.6
  18. 18. Cytopathic Effects of Viruses Table 15.4
  19. 19. Pathogenic Properties of Fungi <ul><li>Fungal waste products may cause symptoms. </li></ul><ul><li>Chronic infections provoke an allergic response. </li></ul><ul><li>Tichothecene toxins inhibit protein synthesis. </li></ul><ul><ul><li>Fusarium </li></ul></ul><ul><li>Proteases </li></ul><ul><ul><li>Candida, Trichophyton </li></ul></ul><ul><li>Capsule prevents phagocytosis. </li></ul><ul><ul><li>Cryptococcus </li></ul></ul><ul><li>Ergot toxin </li></ul><ul><ul><li>Claviceps </li></ul></ul>
  20. 20. Pathogenic Properties of Fungi <ul><li>Aflatoxin </li></ul><ul><ul><li>Aspergillus </li></ul></ul><ul><li>Mycotoxins </li></ul><ul><ul><li>Neurotoxins: Phalloidin, amanitin </li></ul></ul><ul><ul><ul><li>Amanita </li></ul></ul></ul>
  21. 21. Pathogenic Properties of Protozoa <ul><li>Presence of protozoa. </li></ul><ul><li>Protozoan waste products may cause symptoms. </li></ul><ul><li>Avoid host defenses by </li></ul><ul><ul><li>Growing in phagocytes </li></ul></ul><ul><ul><li>Antigenic variation </li></ul></ul>
  22. 22. Pathogenic Properties of Helminths <ul><li>Use host tissue. </li></ul><ul><li>Presence of parasite interferes with host function. </li></ul><ul><li>Parasite's metabolic waste can cause symptoms. </li></ul>
  23. 23. Pathogenic Properties of Algae <ul><li>Paralytic shellfish poisoning </li></ul><ul><ul><li>Dinoflagellates </li></ul></ul><ul><li>Domoic acid intoxication </li></ul><ul><ul><li>Diatoms </li></ul></ul>Figure 27.15
  24. 24. Portals of Exit <ul><li>Respiratory tract </li></ul><ul><ul><li>Coughing and sneezing </li></ul></ul><ul><li>Gastrointestinal tract </li></ul><ul><ul><li>Feces and saliva </li></ul></ul><ul><li>Genitourinary tract </li></ul><ul><ul><li>Urine and vaginal secretions </li></ul></ul><ul><li>Skin </li></ul><ul><li>Blood </li></ul><ul><ul><li>Biting arthropods and needles or syringes </li></ul></ul>
  25. 25. Mechanisms of Pathogenicity Figure 15.9

×