Bacterial Pathogenesis 1 & 2 Flashcards
What are Koch’s postulates?
- organism found in all patients with the disease
- distribution corresponds to lesions
- cultivate outside host for several generations
- reproduce the disease in other species
- demonstrate a specific immune response
What are the key attributes of pathogens?
colonisation, penetration, multiplication, tissue damage
What must a pathogen do to infect a mucosal surface?
overcome competition from commensals, move through mucus, resist mucosal defences and adhere to epithelial cells
How do bacteria adhere to epithelial cells?
fimbriae or non fimbriate adhesins interact with receptors on host cells
How do bacteria penetrate epithelium?
often host cells take up bacteria - pathogen mediated endocytosis
What are pyogenic bacteria?
Bacteria that evade phagocytosis
What are intracellular pathogens?
Pathogens that resist killing
How do pyogenic bacteria evade phagocytosis?
Either by directly attacking phagocytes or by interfering with opsonins
How do capsules protect bacteria?
By preventing them being opsonised
How do antibodies overcome capsule?
Antibodies can bind to the capsule and once antibodies are bound then opsonisation can occur
How do capsules enhance virulence?
electrostatic repulsion, resembling host components, masking underlying PAMPs
How do intracellular pathogens resist phagocytosis?
By inhibiting reparatory burst, preventing phagolysosome formation, escaping from phagocytic vacuole and resisting bactericidal systems
How do pathogens overcome the adaptive immune system?
Direct immunosupression, expression of weak antigens, antigenic diversity, antigen modification
What are the differences between bacterial exotoxins and endotoxins?
- exotoxins are actively produced by living bacteria but endotoxins are produced by the cell wall of dying bacteria
- exotoxins are a protein but endotoxins are a lipopolysaccharide
- exotoxins are sometimes heat resistant but endotoxins are always heat resistant
- exotoxins can be neutralised by antibodies but endotoxins can’t
- you can produce toxoids from exotoxins but not endotoxins
What is the site of action of exotoxins?
can be intracellular or extracellular
