MOD 11 & 12 - Micro-organism in Disease

Question 1

definition of pathogenicity

Answer 1

capacity of a micro-organism to cause an infection

Question 2

what are the 4 main criteria which makes up the pathogenicity

Answer 2

Transmissibility
Establishment in or on a host
Harmful effect(s)
Persistence

Question 3

definition of virulence

Answer 3

the degree to which a micro-organism is able to cause disease

Question 4

definition of infectivity

Answer 4

the ability of a micro-organism to become established on/in a host

Question 5

how can micro-organism become established in a host

Answer 5

through ligand-receptor binding eg E.coli fimbriae - glycolipids on human uroepithelial cells

Question 6

what are virulence factors?

Answer 6

components of micro-organisms which result in harmful effects

Question 7

what are some of the examples of virulence mechanisms

Answer 7

1 - facilitation of adhesion 2 - toxic effect
3 - interference with hot defence mechanisms
4 - tissue damage
5 - facilitation of invasion
6 - modulation of the host cytokine responses `

Question 8

what are the 2 virulence factors for bacteria?

Answer 8

Endotoxin, Extotoxin

Question 9

what is endotoxin

Answer 9

component of gram -ve bacteria cell wall eg E.coli & neisseria meningitis

Question 10

how can endotoxin cause damage

Answer 10

released from damaged/dead cells & have lipopolysaccharide - binds to a number of host cell receptors & induce a range of uncontrolled host response

Question 11

what are the responses of the host

Answer 11

Systemic inflammatory response syndrome (SIRS)

• Uncontrolled T-lymphocyte response (fever, hypotension, tachycardia, cardiac failure)
• Uncontrolled activation of the clotting cascade - bleeding tendency & depletion of clotting factors
• Uncontrolled activation of complement

Question 12

what are exotoxins

Answer 12

proteins produced by living bacteria

Question 13

what is an example of a bacteria for exotoxin production

Answer 13

botulism - clostridium botulinum - contaminated food, infection of dirty wounds, GI colonisation

Question 14

how can botulism cause damage to the body

Answer 14

by releasing exotoxin - which inhibit the release of ACH in neuromuscular junction - ie no muscle contraction

Question 15

what are the clinical presentation of botulism

Answer 15

diplopia, dysphagia, dysarthria, dry mouth, death (respiratory failure)

Question 16

what is Tetanus an example of endotoxin or exotoxin

Answer 16

exotoxin

Question 17

what causes tetanus

Answer 17

clostridium tetani - infection of dirty wounds

Question 18

how can tetanus cause damage to the body

Answer 18

tetanospasmin (toxin) - binds to erve synapses - inhibits release of inhibitory neurotransmitters in CNS (can cause death by respiratory paralysis)

Question 19

what special virulence factor does streptococcus pyogenes have?

Answer 19

VF prmotes connective tissue breakdown and invasion

Question 20

what can streptococcus pygenes cause

Answer 20

strep. pyogenes syndromes - streptococcal sore throat, erysipelas (large raised red patches on the skin), necrotising fasciitis, scarlet fever