Micro-organisms in disease (11 and 12) Flashcards Preview

EMS - Mechanisms of Disease > Micro-organisms in disease (11 and 12) > Flashcards

Flashcards in Micro-organisms in disease (11 and 12) Deck (39):
1

Pathogenicity

Capacity of a micro-organism to cause an infection (transmissibility, establishment in/on a host, harmful effect, persistence)

2

Virulence

(Same as pathogenicity) degree to which micro-organism is able to cause disease

3

Koch's postulates (1890)

- Organism should be present in disease but not in health.
- Organism should be isolated from the diseased animal and grown in pure culture
- Organism should cause the same disease in a newly inoculated animal.
- Organism should be re-isolated from the experimentally-infected animal.

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Infectivity

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

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Examples of ligand-receptor interactions

E. coli P fibmriae: glycolipids on human uroepithelial cells

S.pyogenes protein-F: fibronectin

Influenza haemagglutinin: respiratory epithelial sciali acid receptors

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Virulence factors

Components of micro-organisms that result in harmful effects

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Virulence mechanisms

Facilitation of adhesion, toxic effect, tissue-damage, interference with host defence mechanism, facilitation of invasion, modulation of the host cytokine responses

8

Virulence factors are sometimes referred to as

Adhesins, aggressin,s interferins, moduliun

9

Virulence factors are encoded by

Virulence genes

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Endotoxin

Component of gram negative bacterial cell wall, released from damaged/deal cells, binds to a number of host cell receptors

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What is active component of an endotoxin?

Lipopolysaccharide (LPS)

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Examples of bacteria that have endotoxins

E.coli and other gram-negative bacilli, Neisseria meningitidis

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What is hosts response to an endotoxin?

Systemic inflammatory response syndrome (SIRS)

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What happens in SIRS?

Uncontrolled T-lymphocyte response, uncontrolled activation of the clotting cascade, uncontrolled activation of complement

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What happens in uncontrolled T-lymphocyte response?

- Cytokine release (TNF-a, y-interferon, IL-1)
- Fever, rigor, hypotension, tachycardia, collapse
- Cardiac and/or renal failure

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What happens in uncontrolled activation of the clotting cascade?

Disseminated intravascular coagulation (DIC), depletion of clotting factors, bleeding tendency

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What is Waterhouse-Friedrichsen syndrome?

Meningococcal infection > bilateral adrenal haemorrhage > adrenal failure (due to endotoxin Neisseria meningitidis)

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Exotoxins

Proteins produced by living bacteria, usually have quite specific effects on host

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What micro-organism causes Botulism?

Clostridium botulinum (obligate anaerobe)

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What causes Botulism?

Ingestion of pre-formed toxin (food) or infection of dirty wounds

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Where to Botulism toxin colonise?

GI (infants)

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Symptoms of Botulism

Diplopia, dysphagia, dysarthria, dry mouth, death, respiratory failure (no muscle contraction)

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What micro-organism causes Tetanus?

Clostridium tetani (obligate anaerobe)

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What causes Tetanus?

Infection of dirty wounds

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What toxin does Tetanus produce?

Tetanospasmin

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Tetanospasmin

Produced on germination of spores, binds to nerve synapses, inhibits release of inhibitory neurotransmitters in CNS

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How does death occur in tetanus?

Respiratory paralysis

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Opisthotonos

Spasm of muscles > backward arching of head, neck and spine

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Other exotoxin-mediated infections:

Cholera – Vibrio cholera

Diphtheria – Corynebacterium diphtheria

Clostridium difficile infection – diarrhoea/colitis

E. coli O157 haemorrhagic colitis (verotoxin)

Staphylococcal scalded skin syndrome – Staph. aureus

Whooping cough (pertussis) – Bordetella pertussis

Scarlet fever – Streptococcus progenies

Scalded-skin syndrome – Staph. aureus epidermolysin

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Streptococcus pyogenes

Promote connective tissue breakdown and invasion

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Streptococcus pyogenes syndromes

Streptococcal sore throat, Erysipelas, Necrotising fascilits (soft tissue infection), Scarlet fever

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Streptococcus pyogenes virulence factors

- Hyaluronidase and streptokinase (break down connective tissue)
- C5a peptidase (inactivates C5a)
- Streptolysins -O and -H (lyse RBC, WBC, platelets)
- Erythrogenic toxin (rash scarlet fever)
- Toxic shock syndrome toxin

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Necrotising fascilitis

Pain, black areas of inflammation/dead tissue, very sick, antibiotics insufficient, have to remove infected tissue (debriding)

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Which micro-organisms inhibit phagocytosis?

S. pyogenes and S. pneumoniae

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S. pyogenes inhibit phagocytosis by

M-protein binds fibrinogen and masks bacterial surface, blocking complement binding and opsonisation

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S. pneumoniae inhibit phagocytosis by

Polysaccharide capsule inhibits opsonisation and therefore phagocytosis

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Intracellular pathogens

Mycobacterium TB, Salmonella typhi, Listeria monocytogenes

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What is whole virus particle called?

A virion

39

Virus life cycle

1. Adsorption (stick on cell)
2. Penetration (endocytosis)
3. Uncoating (genetic material released)
4. Synthesis
5. Assembly
6. Release (budding/cell burst)