Factors in Infection

Question 1

How is the infectious dose important in infection?

Answer 1

There is a minimum number of organisms required to produce disease

Question 2

How is ebola different to most infections?

Answer 2

Often bypasses steps of immune system and causes direct infection

Question 3

How does streptolycin O affects cells? What type of infection is it?

Answer 3

Virus

Lyses cells by damaging membrane by producing cytolysin

Question 4

What is cytolysin?

Answer 4

Substance secreted by microorganisms that is specifically toxic to cells, causing their dissolution through lysis

Question 5

What is the mechanism by which cholera toxin acts?

Answer 5

1. Bacteria produce toxic which enters cells of gut lumen
2. Activates adenyl cyclase, increasing cAMP
3. Reduces Na+ absorption
4. Increases Cl- secretion
5. Water and electrolytes drawn into bowel lumen

Question 6

What is symptoms and dangers of cholera?

Answer 6

Diarrhoea - Causes severe dehydration, kidney failure, death due to massive loss of water and electrolytes

Question 7

What is danger of overusing antibiotics?

Answer 7

Microorganisms readily mutate to escape antibiotic use. More antibiotics = more mutations leading to failure of antibiotic treatment

Question 8

What are features of MRSA?

Answer 8

Gram-positive bacteria causing severe infections in hospital due to resistance

Question 9

How does stomach acid provide a barrier to infection?

Answer 9

pH 2 - very few organisms survive this

Question 10

Why are patients taking drugs for stomach ulcers more susceptible to food poisoning?

Answer 10

Drugs increase stomach pH - less organisms killed

Question 11

How does normal gut flora provide a barrier to infection?

Answer 11

Prevents colonisation by pathogenic bacteria

Question 12

Why do antibiotics increase susceptibility to some diseases?

Answer 12

Antibiotics kill ‘friendly’ bacteria which allows pathogens to reproduce and cause disease

Question 13

What is an example of a disease caused by antibiotic treatment?

Answer 13

Diarrhoea due to C. diff

Question 14

What is C. diff?

Answer 14

Bacteria that infect bowel and cause diarrhoea. The infection most commonly affects people recently treated with antibiotics

Question 15

How does HIV affect the immune system?

Answer 15

Infects white cells which control immune system. Makes most infections more common and severe. Causes infections by opportunistic microorganisms

Question 16

What are opportunistic microorganisms?

Answer 16

Microorganisms that don’t usually cause disease

Question 17

What are autoimmune diseases?

Answer 17

Overactive immune systems - thinks own body cells are foreign

Question 18

How does active immunisation work?

Answer 18

Stimulating immune system with something that mimics infection e.g. Hep B virus surface antigen