Flashcards in L11&12- Micro-Organisms in Disease Deck (12):
What is Virulence ?
the degree to which a micro-organism is able to cause disease
E.g: S. aureus is more virulent than S. viridans, as it causes disease much more readily.
Koch’s postulates (Do we need to know?)
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.
What is Infectivity ?
The ability of a micro-organism to become established on/in a host
Virulence factor: Endotoxin ...What is it?
Component of the Gram-negative bacterial cell wall
E.g: E. coli and other Gram-negative bacilli
Active component is lipopolysaccharide - LPS
Induces a range of uncontrolled host responses
Endotoxin: host response - What can happen?
Systemic inflammatory response syndrome (SIRS):
-Uncontrolled T-lymphocyte response
-Uncontrolled activation of the clotting cascade
-Uncontrolled activation of complement
Botulinum toxin effects
-Neurotoxic protein produced by the bacterium Clostridium botulinum (obligate anaerobe)
-Affect Neuromuscular junction- prevents muscle contraction
-prevents the release of acetylcholine
Clostridium tetani (obligate anaerobe) - toxin effects
-Produced on germination of spores
-Binds to nerve synapses
-Inhibits release of inhibitory neurotransmitters (e.g. gamma-amino butyric acid) in the central nervous system
-Death caused by respiratory paralysis
Meaning of Opisthotonus/opisthotonos
State of severe hyperextension and spasticity in which an individual's head, neck and spinal column enter into a complete "bridging" or "arching" position
(Happens with Clostridium tetani)
Streptococcus pyogenes can cause conditions such as:
Streptococcal sore throat
-Strep. pyogenes has virulence factors that promote connective tissue breakdown and invasion
Examples of how some bacteria can evade the immune system...
S. Pyogenes: M-protein binds fibrinogen and masks bacterial surface, blocking complement binding and opsonisation
S. pneumoniae: Polysaccharide capsule inhibits opsonisation and therefore phagocytosis1
Brief overview of viruses
Small particles consisting of up to three components:
1) Genome - RNA or DNA
2) Capsid - protein
3) (Envelope – lipid bilayer)
Whole particle is called a virion
Not capable of independent existence
Use host mechanisms to satisfy the requirements of growth and replication