pathogenicity

• Portals of entry


  Points at which pathogens enter the body
• Pathogenicity


  Likelihood of causing disease
• Virulence


  Measure of the pathogen's destructive capacity
• Portals of exit


  Points at which pathogens leave the body
• Capsules

  • Protective outer layer of some bacteria
• M protein of Streptococcus


  • Facilitates attachment and resists phagocytosis
• Fimbriae


  • Hair-like structures that aid in attachment, e.g., Neisseria gonorrhoeae
• Cell walls


  • Provide protection, e.g., Mycobacteria resist phagocytosis
• Exotoxins

  Proteins that are heat-labile, with high toxicity; often A-B toxins
• Cytotoxins


  Kill cells, e.g., diphtheria toxin inhibits protein synthesis
• Neurotoxins


  Affect nerve cells, e.g., botulinum toxin inhibits acetylcholine release
• Enterotoxins


  Target intestinal epithelia, causing electrolyte and water loss
• Endotoxins


  Lipid A component of LPS in Gram-negative bacteria, causing septic shock
• Superantigens


  Stimulate T cell proliferation and cytokine release, e.g., Streptococcus pyogenes and Staphylococcus aureus