11,12 - Microorganisms in Disease

Question 1

virulence definition

Answer 1

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

Question 2

LD/ID50 stands for

Answer 2

Lethal/infectious doses

Question 3

Infectivity - how?

Answer 3

Microbial ligant

Host cell surface receptor

Question 4

Virulence factors

Answer 4

Facilitation of adhesion
Toxic effect
Tissue-damage
Interference with host defence mechanisms
Facilitation of invasion
Modulation of the host cytokine resopnses

Namely, adhesins, aggressins, interferins, modulins

Question 5

What are endotoxins?

Answer 5

Components of gram–ve bacterial cell wall: E.Coli, neisseria meningitidis

released from dmged/dead cells

Active component is lipopolysaccharide

Binds to number of host cell receptors inducing range of uncontrolled host responses

Question 6

Host response to endotoxins

Answer 6

SIRS

Question 7

What is SIRS?

Answer 7

Uncontrolled T-lymphocyte response: cytokines (TNF-a, y-IFN, IL-1); fever, rigors, tachycardia, collapse –> cardiac/renal failure

Uncontrolled clotting cascade = DIC, clotting factor depletion + bleeding tendency

Uncontrolled complement activation

Question 8

If a shock response is to increase permeability etc why do we get vasoconstriction?

Answer 8

Leakage of protein, fluid and plasma into tissues causes pathological compensatory vasoconstriction

Question 9

Exotoxins

Answer 9

protein produced by living bacteria - quite specific effect on host

Question 10

Botulism - clinical presentation

Answer 10

Diplopia 
Dysphagia
Dysarthria
Dry mouth
Death - via resp. failure

Question 11

What is the toxin produced by tetanus?

Answer 11

Tetanospasmin

Produced on spore germination, binds to nerve synapses and inhibits neuro-trans

Causes death by resp. paralysis

Question 12

what causes scarlet fever?

Answer 12

Strep. pyogenes

Question 13

What does strep pyogenes do?

Answer 13

has virulence factors that promote connective tissue breakdown and invasion

Question 14

Strep. pyogenes syndromes

Answer 14

Strep sore throat
Erysipelas
Necrotising fasciitis
Scarlet fever

Question 15

S.pyogenes virulence factors

Answer 15

Hyaluronidase and streptokinase (connective tissue breakdown)

C5a peptidase (inactivates C5a)

Streptolysins -O and -H (lyse R/W BCs and platelets)

Erythrogenic toxin (scarlet fever rash)

Toxic shock syndrome toxin (strep toxic shock syndrome is superficially similar to a syndrome of endotoxin release)