11,12 - Microorganisms in Disease Flashcards Preview

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Flashcards in 11,12 - Microorganisms in Disease Deck (15):
1

virulence definition

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

2

LD/ID50 stands for

Lethal/infectious doses

3

Infectivity - how?

Microbial ligant
Host cell surface receptor

4

Virulence factors

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

5

What are endotoxins?

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

6

Host response to endotoxins

SIRS

7

What is SIRS?

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

8

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

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

9

Exotoxins

protein produced by living bacteria - quite specific effect on host

10

Botulism - clinical presentation

Diplopia
Dysphagia
Dysarthria
Dry mouth
Death - via resp. failure

11

What is the toxin produced by tetanus?

Tetanospasmin

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

Causes death by resp. paralysis

12

what causes scarlet fever?

Strep. pyogenes

13

What does strep pyogenes do?

has virulence factors that promote connective tissue breakdown and invasion

14

Strep. pyogenes syndromes

Strep sore throat
Erysipelas
Necrotising fasciitis
Scarlet fever

15

S.pyogenes virulence factors

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)