microbiology ch. 15 & 16

• What is adherence?

  When almost all pathogens attach to host tissues
• Why is adherence important for pathogenesis?

  • It is the primary determinant of treatment success
• What structures does adherence interact with?

  • Strep. Mutans- Glycocalyx adhesions
• What are biofilms composed of?

  communities that share nutrients and adhere to surface
• How do biofilms contribute to disease?

  • Protect microorganisms against the host immune system
• Where are biofilms found?

  • Found in hospital wastewater, left-over drugs, and medical instruments
• Factors that contribute to virulence

  • Capsules
  • Cell wall components
  • Enzymes
  • Antigenic variation
  • Penetration into host cell cytoplasm
• Capsules

  Prevent phagocytosis by preventing phagocytic cells from adhering
• Example of capsule

  • Pneumoniae- pneumonia
• Cell wall components

  Help resist phagocytosis
• example of cell wall components

  • Strep. Pyogenes
• Enzymes

  Damage host tissues
• Example of enzymes

  • Coagulase
• Antigenic variation

  Pathogens alter their surface antigens
• Example of antigenic variation

  • Trypanosomes
• Penetration into host cell cytoplasm

  Rearrange actin filaments of the cytoskeleton
• example of Penetration into host cell cytoplasm

  • Shigella
• Exotoxins

  Proteins produced and secreted by bacteria or released upon lysis of bacteria
• Endotoxins

  Released during bacterial multiplication and when gram-neg bacteria die
• Types of Exotoxins

  • A-B toxins
  • Membrane disrupting toxins
  • Superantigens
• A-B toxins

  Contain an enzyme (A) and binding site (B)
• Membrane disrupting toxins

  Lyse host cells by disrupting plasma membrane or to allow for escape from phagosomes
• Superantigens

  Cause an intense immune response due to the release of cytokines from host cells
• Inactivation of exotoxins

  The binding of the exotoxin and antibody forms an antigen-antibody interaction
• What gram cell produces endotoxins?

  Gram-neg
• Innate immunity

  Non-specific and includes 1st and 2nd lines of defense against pathogens
• Adaptive immunity

  Specific and includes the 3rd line of defense
• First line of defense

  • Physical factors: the skin (dermis) & mucous membranes (mucus)
  • Chemical factors: sebum, perspiration, gastric juice, vaginal secretions, & urine
• Leukocytes involved in innate immunity

  • Granulocytes: neutrophils, basophils, eosinophils
  • Agranulocytes: monocytes, dendritic cells, natural killer cells
• Toll-Like Receptors

  Found on defensive cells, bind to pathogens, and play a role in innate immunity
• 7- steps of phagocytosis

  1. Chemotaxis

  2. Attachment

  3. Ingestion

  4. Phagosome formation

  5. Phagolysosome formation

  6. Digestion

  7. Egestion
• 6 ways microbes can evade phagocytosis

  • Avoid adherence
  • Inhibit phagocytosis
  • Resist killing within phagocytes
  • Escape from phagocytes
  • Induce apoptosis of phagocytes
  • Inhibit phagosome-lysosome fusion
• Signs of inflammation

  • Pain
  • Redness
  • Immobility
  • Swelling
  • Heat
• Purpose of inflammation

  Destroy infectious agent and remove byproducts, limit effects on body, and repair and replace tissues damaged by the injurious agent
• 3-steps of inflammation

  1. Chemicals are released by damaged cells.

  2. Blood clot forms

  3. Abscess starts to form
• Ways complement can be activated

  • Classical
  • Alternative
  • Lectin
• Classical complement activation


  Antibodies bind to molecules on the microbe
• Alternative complement activation


  The lipid-carbohydrate complex attracts complement proteins B, D, and P
• Lectin complement activation

  Macrophages ingest pathogens, releasing cytokines that stimulate lectin production in the liver
• Outcomes of complement activation

  • Cytolysis
  • Opsonization
  • Inflammation