Pathogens and Host

Question 1

A clinical infection is characterised by which signs and symptoms? (7)

Answer 1

1. inflammation
2. pain
3. pyrexia (fever)
4. rigors
5. increased WBC count
6. increase C reactive protein
7. tachycardia

Question 2

what is an acute illness/symptoms? examples?

Answer 2

sudden and severe in onset such as asthma or a broken bone

Question 3

what is a latent infection?

Answer 3

infection which is dormant (“sleeping”) and may reappear if activated

Question 4

what is a sub-clinical infection?

Answer 4

asymptomatic infections with no signs or symptoms

Question 5

what is definition of pathogen?

Answer 5

organism which can cause disease

Question 6

what is definition of commensal? what is an example?

Answer 6

organism which is part of the normal flora (e.g. e.coli in the gut or s.aureus in the nose or axilla

Question 7

which patients particularly make it difficult to distinguish between a pathogen and a commensal?

Answer 7

immunosuppressant patients

Question 8

what is meant by Koch’s Postulates?

Answer 8

criteria established by Koch to identify the causative agent of a particular disease

Question 9

what are the 3 Koch’s postulates? (criteria)

Answer 9

1. organisms must be found in all cases of the disease
2. able to be cultured outside the body for several generations
3. should reproduce the disease on inoculation

Question 10

what are the 4 things which should be known when identifying the causative agent of a particular disease?

Answer 10

Knowledge of…

1. sterile/non-sterile sites
2. normal flora of site
3. organism’s pathogenicity
4. clinical context

Question 11

what does host-pathogen interaction depend on?

Answer 11

Patient’s immune system (e.g. pregnant, chronic condition or acute illness all have different immune systems)

Question 12

what is meant by pathogenicity?

Answer 12

the capacity of a micro-organism to cause an infection

Question 13

what are 2 requirements for pathogenicity?

Answer 13

1. virulence

2. infectivity

Question 14

what does virulence mean?

Answer 14

ability to cause harmful effects once pathogen is established

Question 15

what does infectivity mean?

Answer 15

• ability for pathogen to become established

Question 16

what are 2 examples of infectivity mechanisms?

Answer 16

1. attachment (e.coli)

2. acid resistance (helicobacter pylori)

Question 17

what are the 3 virulence factors which are microbial components?

Answer 17

1. invasiveness
2. toxin production
3. evasion of the immune system

Question 18

what is meant by invasiveness?

Answer 18

how fast the pathogen takes over the body

Question 19

what are 3 types of toxins?

Answer 19

1. exotoxin
2. enterotoxin
3. endotoxin

Question 20

what is an exotoxin?

Answer 20

released extracellularly by the micro-organism

Question 21

what is an enterotoxin?

Answer 21

they are exotoxins which act on the GI tract

Question 22

what are endotoxins?

Answer 22

structurally part of the gram negative cell wall (intracellularly) , released from bacteria cell wall

Question 23

what is an example of an exotoxin?

Answer 23

tetanus:
- infection of dirty wounds
- binds to nerve synapses and loss of inhibitory neurotransmitter
- death caused by respiratory paralysis

Question 24

what is an example of an enterotoxin?

Answer 24

cholera;

• food and water contamination
• colonises small intestine
• increases cAMP, inhibits uptake of Na and CL, stimualtes secretion of Cl and HCO3 and outflow of H2O
• death by dehydration

Question 25

where are superantigens found?

Answer 25

in certain exotoxins of strep. pyogenes and staph. aureus

Question 26

what do superantigens do?

Answer 26

• stimulate division of t cells at the ABSENCE of specific antigens
• overwhelming cytokine production is activated causing toxic shock
• t cells are not specific to particular antigens and cause a huge immune response

Question 27

what is an example of an endotoxin?

Answer 27

• e.coli ( and other gram negative bacilli)

- neisseria meningitidis (induces cytokines production)

Question 28

what part of the endotoxin can lead to septic shock?

Answer 28

the lipid component (lipid A) , it’s toxic

Question 29

what are the harmful effects caused by? (3)

Answer 29

1. bacterium
2. the host response
3. both