Flashcards in Micro-organisms in disease (11 and 12) Deck (39):
Capacity of a micro-organism to cause an infection (transmissibility, establishment in/on a host, harmful effect, persistence)
(Same as pathogenicity) degree to which micro-organism is able to cause disease
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.
The ability of a micro-organism to become established on/in a host
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
Components of micro-organisms that result in harmful effects
Facilitation of adhesion, toxic effect, tissue-damage, interference with host defence mechanism, facilitation of invasion, modulation of the host cytokine responses
Virulence factors are sometimes referred to as
Adhesins, aggressin,s interferins, moduliun
Virulence factors are encoded by
Component of gram negative bacterial cell wall, released from damaged/deal cells, binds to a number of host cell receptors
What is active component of an endotoxin?
Examples of bacteria that have endotoxins
E.coli and other gram-negative bacilli, Neisseria meningitidis
What is hosts response to an endotoxin?
Systemic inflammatory response syndrome (SIRS)
What happens in SIRS?
Uncontrolled T-lymphocyte response, uncontrolled activation of the clotting cascade, uncontrolled activation of complement
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
What happens in uncontrolled activation of the clotting cascade?
Disseminated intravascular coagulation (DIC), depletion of clotting factors, bleeding tendency
What is Waterhouse-Friedrichsen syndrome?
Meningococcal infection > bilateral adrenal haemorrhage > adrenal failure (due to endotoxin Neisseria meningitidis)
Proteins produced by living bacteria, usually have quite specific effects on host
What micro-organism causes Botulism?
Clostridium botulinum (obligate anaerobe)
What causes Botulism?
Ingestion of pre-formed toxin (food) or infection of dirty wounds
Where to Botulism toxin colonise?
Symptoms of Botulism
Diplopia, dysphagia, dysarthria, dry mouth, death, respiratory failure (no muscle contraction)
What micro-organism causes Tetanus?
Clostridium tetani (obligate anaerobe)
What causes Tetanus?
Infection of dirty wounds
What toxin does Tetanus produce?
Produced on germination of spores, binds to nerve synapses, inhibits release of inhibitory neurotransmitters in CNS
How does death occur in tetanus?
Spasm of muscles > backward arching of head, neck and spine
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
Promote connective tissue breakdown and invasion
Streptococcus pyogenes syndromes
Streptococcal sore throat, Erysipelas, Necrotising fascilits (soft tissue infection), Scarlet fever
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
Pain, black areas of inflammation/dead tissue, very sick, antibiotics insufficient, have to remove infected tissue (debriding)
Which micro-organisms inhibit phagocytosis?
S. pyogenes and S. pneumoniae
S. pyogenes inhibit phagocytosis by
M-protein binds fibrinogen and masks bacterial surface, blocking complement binding and opsonisation
S. pneumoniae inhibit phagocytosis by
Polysaccharide capsule inhibits opsonisation and therefore phagocytosis
Mycobacterium TB, Salmonella typhi, Listeria monocytogenes
What is whole virus particle called?