10. Micro-organisms in Disease

Question 1

what is pathogenicity?

Answer 1

the capacity of a micro-organism to cause an infection

Question 2

what are the characteristics of a pathogenic organism?

Answer 2

transmissibility
establishment in or on a host
harmful effects
persistence

Question 3

what is virulence?

Answer 3

the degree to which a micro-organism is able to cause disease. allows a relative description of pathogenic potential

Question 4

what is LD50?

Answer 4

dose of an organism that all cause death in 50% of the animals exposed to it

Question 5

what is ID50?

Answer 5

dose of an organism that will cause infection in 50% of the animals exposed to it

Question 6

what is infectivity?

Answer 6

the ability of a micro-organism to become established on or in a host. either accomplished with the help of a microbial ligand or a host cell surface receptor

Question 7

what are virulence factors?

Answer 7

components of micro-organisms that result in harmful effects

Question 8

what are virulence mechanisms of micro-organisms?

Answer 8

facilitation of adhesion (adhesins)
toxic effects (toxins)
tissue damage (aggressins)
interference with host defence mechanisms (interferins)
facilitation of invasion
modulation of the host cytokine responses (modulins)

Question 9

when are endotoxins released?

Answer 9

damaged to dead bacterial cells

Question 10

what is the active component of an endotoxin?

Answer 10

lipopolysaccharide (LPS)

Question 11

how does LPS harm the body?

Answer 11

binds to a number of host cell receptors and induces a range of uncontrolled host responses

Question 12

where are endotoxins found?

Answer 12

bacterial cell wall

Question 13

what is the effect of exotoxins?

Answer 13

systemic inflammatory response syndrome, involving

1. uncontrolled t lymphocyte response
2. uncontrolled activation of the clotting cascade
3. uncontrolled activation of the complement

Question 14

what are the effects of an uncontrolled t lymphocyte response?

Answer 14

cytokine release
fever, riggers, hypotension, tachicardia, collapse
cardiac and/or renal failure

Question 15

what are the effects of uncontrolled activation of the clotting cascade

Answer 15

disseminated intravascular coagulation (DIC)
depletion of clotting factors
bleeding tendency

Question 16

where are exotoxins food and how can they be tackled?

Answer 16

produced by living bacteria

patients can be treated by actually killing the bacteria

Question 17

which organism causes botulism?

Answer 17

clostridium botulinum

Question 18

how does c. botulinum spread?

Answer 18

ingestion of pre-formed toxin
infection of dirty wounds
GI colonisation in infants

Question 19

what are the effects of botulism?

Answer 19

causes flaccid paralysis because it blocks muscle contraction

Question 20

what is the clinical presentation of botulism?

Answer 20

diplopia
dysphagia
dysarthria
dry mouth
death due to respiratory failure

Question 21

what organism causes tetanus?

Answer 21

clostridium tetani

Question 22

what toxin is produced in tetanus?

Answer 22

tetanospasmin

Question 23

what are the effects of tetanospasmin?

Answer 23

binds to nerve synapse, inhibits release of inhibitory neurotransmitters in the CNS
eventually leads to death due to respiratory paralysis

Question 24

what are the effects of strep. progenies virulence factors?

Answer 24

promote connective tissue breakdown and aids invasion

Question 25

what are the syndromes caused by strep. pyogenes?

Answer 25

streptococcal sore throat
erysipelas
necrotising fasciitis
scarlet fever

Question 26

how does s. pyogenes evade the immune system?

Answer 26

m protein binds to fibrinogen and masks the bacterial surface, blocking complement binding and opsonisation

Question 27

how does s. pneumoniae evade the immune system?

Answer 27

its polysaccharide capsule inhibits opsonisation and therefore phagocytosis

Question 28

which pathogens are intracellular?

Answer 28

mycobacterium tuberculosis
salmonella typhi
listeria monocytogenes