THEME 6

• Pathogen: organism that grows/on a host and causes disease.
• Pathogenicity: the ability of a pathogen to cause disease
• Virulence: measure of pathogenicity
• Virulence factors: factors/strategies used by bacteria to cause disease
• Compromised host: a host w/ low resistance (HIV/Cancer patient)
• Opportunistic pathogen: causes disease only in the absence of normal host resistance
• Attenuation: the decrease/ loss of virulence.
• Toxicity: organism causes disease by means of a toxin that inhibits host cell function/ kills cell (toxins travel to sites, pathogen not inside host).
• Effector: secretion & translocated virulence factors that interfere w/ host defence.
• Compatible: pathogen can cause disease.
• Entry of pathogen:

  • Human: nose, urogenital, mouth, wounds, mucous membranes, bites.
  • Plants: stomata, hydrathodes, lenticels, wounds, bites
• Bacterial adherence facilitated by:

  • Extracellular macromolecules (not covalently attached to bacterial cell surface, eg. Slime layer)
  • Adhesins
  • Fimbriae and pili
  • Flagella
• Virulence factors:

  Tissue damaging enzymes

  Plant cell wall degrading enzymes

  Endo- and exo- toxins
• Tissue damaging enzymes: Coagulase:

  • Produced by pus forming Staphylococcus aureus Human microbiota (upper respiratory tract and skin) - induced fibrin clotting - Localized - Protects pathogen from host immunity
• Tissue damaging enzymes: Streptokinase

  • Produced by pus forming Streptococcus pyogenes
  • Skin microbiota
  • Pathogenic
  • dissolves clot
  • allows bacteria to spread into blood and deep tissue
  • systemic.
• Tissue damaging enzymes: Hyaluronidase

  Produced by pus forming Streptococcus pyogenes

  - dissolves hyaluronic acid in connective tissue

  - allows bacteria to spread

  -systemic
• Plant cell wall degrading enzymes

  Type II secretion system: pectinase, cellulase, protease
• Exotoxins: Proteins released from the pathogen cell as it grows.