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Mechanisms of Pathogenicity

Mechanisms of Pathogenicity. Microbiology 2314. Definitions. Pathogenicity The ability of a pathogen to produce a disease by overcoming the defenses of the host. Virulence The degree of pathogenicity Portal of Entry The specific route by which a particular

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Mechanisms of Pathogenicity

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  1. Mechanisms of Pathogenicity Microbiology 2314

  2. Definitions • Pathogenicity The ability of a pathogen to produce a disease by overcoming the defenses of the host. • Virulence The degree of pathogenicity • Portal of Entry The specific route by which a particular pathogen gains access to the body.

  3. Portals of Entry

  4. Preferred Portal of Entry • Many microorganisms can cause infections only when they gain access through their specific portal of entry. • If they enter via another portal they cause no response. • Example: Flu is specific for respiratory tissues and cannot cause disease if it enters a different portal.

  5. Virulence Can Be Expressed By the Numbers of Invading Microbes • LD50 - The number of microbes in a dose that will kill 50% of inoculated test animals.

  6. ID50 - The dose required to produce a demonstratable infection in 50% of the test animals

  7. Question? • Agent A has a LD50 of 3. • Agent B has a LD50 of 3000. Which is the more virulent?

  8. Remember: The Likelihood of Disease Increases as the Number of Invading Microbes Increases Capsules Aid in Colonizing a Host • Resist Phagocytosis • Increase Adherence • Streptococcus pneumoniae • Klebsiella pneumonia • Baillus anthracis • Yersinia pestis

  9. Proteins in the Cell Wall Can Facilitate Adherence or Prevent a Pathogen From being Phagocytized These Are Called M-Proteins

  10. Bacteria Also Produce Enzymes To Aid in Colonization • Leukocidins / Destroy WBC - Staphylococci and Streptococci • Hemolysins / Lyse RBC - C. perfringens, Staphylococci, Streptococci • Fibrin Clot / Formed By Coagulase - Staphylococci • Kinases / Destroy Blood Clots - S. pyogenes, S. aureus

  11. Microbial Colonization Can Result In Cell Damage and Death • Direct Damage Host cells can be destroyed via pathogens multiplying and being released.

  12. Production of Toxins by Microbes • Toxins Poisonous Substances • Toxemia Presence of Toxins in the Blood • Toxigenicity Ability to Produce Toxins

  13. Exotoxins • Exotoxins Produced Inside the Bacteria as Part of their Growth and Released into the Surrounding Medium

  14. Streptococcal pyrogenic exotoxins A (SPE-A) and B (SPE-B) have been implicated in the pathogenesis of serious group A streptococcal infections including streptococcal toxic shock-syndrome. • Clostridium difficile produces large oval subterminal spores and two different toxins; toxin A (an exotoxin causing fluid accumulation in the intestine) and toxin B (a cytopathic agent).

  15. Endotoxins • Endotoxins A Structural Component in the Bacteria That is Toxic and Released When the Bacterial Cell Dies and in Lysed • For example, the endotoxin of Bacillus thuringiensis makes crystal-like inclusion bodies next to the endospore inside the bacteria. It is toxic to larvae of insects feeding on plants, but is harmless to humans.

  16. Endotoxins Result In • Fever • Chills • Weakness • Aches • Miscarriage • Shock • Death

  17. Antitoxins • Antibodies Produced Against Exotoxins • An antitoxin is an antibody with the ability to neutralize a specific toxin. Antitoxins are produced by certain animals, plants, and bacteria. Although they are most effective in neutralizing toxins, they can kill bacteria and other microorganisms.

  18. Cytotoxins Work by Destroying Particular Parts of the Hosts Cell or by Inhibiting Metabolic Functions (Ulcers) • Neurotoxins Inhibit or Prevent Nerve Transmission (Tetanus) • Enterotoxins Induce Fluid and Electrolyte Loss from Host Cells (Cholera)

  19. Viruses Avoid the Host’s Immune Response by Growing Inside Cells.

  20. Visible Indications of Viral Infections are Called Cytopathic Effects • Stopping Mitosis • Lysis • Formation of Inclusion Bodies • Cell Fusion • Chromosomal Changes • Cytocidal Effects (Cell Death) • Noncytocidal Effects (Cell Damage but not Death)

  21. Fungi, Protozoa, Helminthes, & Algae • Symptoms Caused by 1. Capsules 2. Toxins 3. Allergic Reactions • Resulting In 1. Damage to Host Tissue 2. Poisoning by Metabolic Wastes

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