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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. ID 50 : Infectious dose for 50% of the test population

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Microbial Mechanisms of Pathogenicity

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  1. Microbial Mechanisms of 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 • 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. Penetration of Host • Capsule • Components of the Cell Wall • Enzymes • Antigenic Variation • Cytoskeletal components

  8. Enzymes • Coagulase Coagulates blood • Kinases Digest fibrin clots • Hyaluronidase Hydrolyses hyaluronic acid • Collagenase Hydrolyzes collagen • IgA proteases Destroy IgA antibodies

  9. How Pathogens Damage Host Cells • Use of Host Nutrients • Siderophores • Direct Damage • Production of Toxins • Hypersensitivity Reaction

  10. 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

  11. Endotoxin Figure 15.4b

  12. Endotoxins Figure 15.6

  13. Endotoxins

  14. Exotoxins Figure 15.4a

  15. Exotoxin

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

  17. 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

  18. 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

  19. Exotoxins

  20. Cytopathic Effects of Viruses Table 15.4

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

  22. Mechanisms of Pathogenicity Figure 15.9

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