Module 12: Infectious Disease

• commensal pathogen: part of normal microbiota, causes disease under some conditions
• opportunistic pathogen: causes disease in compromised hosts
• primary pathogen: causes disease in healthy people
• Koch's postulates:

  1. pathogen present in all cases of disease and absent in healthy animals
  2. pathogen must grow in pure culture
  3. cells from pure culture must cause disease in healthy animal
  4. reisolated pathogen must be same as original
• label the steps of disease

  A) attachment

  B) invasion

  C) growth and colonization

  D) damage

  
• pathogen attachment: specific to receptor/surface
• pathogen invasion: enter epithelial cells or loose junctions and move between cells
• which step is not required to cause disease?

  pathogen invasion
• what types of pathogens go through invasion?

  facultative and obligate intracellular pathogens
• growth and colonization: acquire nutrients (iron), requires appropriate environmental conditions
• how do extracellular pathogens acquire nutrients?

  secrete hydrolytic enzymes
• how do intracellular pathogens acquire nutrients?

  from host cell cytoplasm
• reservoir: site where pathogen remains viable and can infect individuals
• what are examples of reservoirs?

  • environment: soil, water, plants
  • other animals
  • humans
• exotoxin: secreted toxin with specific host cell target
• what are the subunits of exotoxin and their purpose?

  A subunit: toxic activity

  B subunit: binding to target cells
• endotoxin: lipopolysaccharide, induce immune response