Bacterial Pathogenesis 1 & 2

Question 1

What are Koch’s postulates?

Answer 1

• 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

Question 2

What are the key attributes of pathogens?

Answer 2

colonisation, penetration, multiplication, tissue damage

Question 3

What must a pathogen do to infect a mucosal surface?

Answer 3

overcome competition from commensals, move through mucus, resist mucosal defences and adhere to epithelial cells

Question 4

How do bacteria adhere to epithelial cells?

Answer 4

fimbriae or non fimbriate adhesins interact with receptors on host cells

Question 5

How do bacteria penetrate epithelium?

Answer 5

often host cells take up bacteria - pathogen mediated endocytosis

Question 6

What are pyogenic bacteria?

Answer 6

Bacteria that evade phagocytosis

Question 7

What are intracellular pathogens?

Answer 7

Pathogens that resist killing

Question 8

How do pyogenic bacteria evade phagocytosis?

Answer 8

Either by directly attacking phagocytes or by interfering with opsonins

Question 9

How do capsules protect bacteria?

Answer 9

By preventing them being opsonised

Question 10

How do antibodies overcome capsule?

Answer 10

Antibodies can bind to the capsule and once antibodies are bound then opsonisation can occur

Question 11

How do capsules enhance virulence?

Answer 11

electrostatic repulsion, resembling host components, masking underlying PAMPs

Question 12

How do intracellular pathogens resist phagocytosis?

Answer 12

By inhibiting reparatory burst, preventing phagolysosome formation, escaping from phagocytic vacuole and resisting bactericidal systems

Question 13

How do pathogens overcome the adaptive immune system?

Answer 13

Direct immunosupression, expression of weak antigens, antigenic diversity, antigen modification

Question 14

What are the differences between bacterial exotoxins and endotoxins?

Answer 14

• 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

Question 15

What is the site of action of exotoxins?

Answer 15

can be intracellular or extracellular

Question 16

What is the mechanism of exotoxins?

Answer 16

Can be cytotoxic (inhibitory) or cytotonic (stimulatory)

Question 17

Name an intracellular cytotoxic exotoxin

Answer 17

diptheria toxin or shiga toxin

Question 18

What is the structure and action of diphtheria toxin?

Answer 18

A and B subunits - the B subunit binds and the A subunit acts