MOD 11 & 12 - Micro-organism in Disease Flashcards
definition of pathogenicity
capacity of a micro-organism to cause an infection
what are the 4 main criteria which makes up the pathogenicity
Transmissibility
Establishment in or on a host
Harmful effect(s)
Persistence
definition of virulence
the degree to which a micro-organism is able to cause disease
definition of infectivity
the ability of a micro-organism to become established on/in a host
how can micro-organism become established in a host
through ligand-receptor binding eg E.coli fimbriae - glycolipids on human uroepithelial cells
what are virulence factors?
components of micro-organisms which result in harmful effects
what are some of the examples of virulence mechanisms
1 - facilitation of adhesion 2 - toxic effect
3 - interference with hot defence mechanisms
4 - tissue damage
5 - facilitation of invasion
6 - modulation of the host cytokine responses `
what are the 2 virulence factors for bacteria?
Endotoxin, Extotoxin
what is endotoxin
component of gram -ve bacteria cell wall eg E.coli & neisseria meningitis
how can endotoxin cause damage
released from damaged/dead cells & have lipopolysaccharide - binds to a number of host cell receptors & induce a range of uncontrolled host response
what are the responses of the host
Systemic inflammatory response syndrome (SIRS)
- Uncontrolled T-lymphocyte response (fever, hypotension, tachycardia, cardiac failure)
- Uncontrolled activation of the clotting cascade - bleeding tendency & depletion of clotting factors
- Uncontrolled activation of complement
what are exotoxins
proteins produced by living bacteria
what is an example of a bacteria for exotoxin production
botulism - clostridium botulinum - contaminated food, infection of dirty wounds, GI colonisation
how can botulism cause damage to the body
by releasing exotoxin - which inhibit the release of ACH in neuromuscular junction - ie no muscle contraction
what are the clinical presentation of botulism
diplopia, dysphagia, dysarthria, dry mouth, death (respiratory failure)
what is Tetanus an example of endotoxin or exotoxin
exotoxin
what causes tetanus
clostridium tetani - infection of dirty wounds
how can tetanus cause damage to the body
tetanospasmin (toxin) - binds to erve synapses - inhibits release of inhibitory neurotransmitters in CNS (can cause death by respiratory paralysis)
what special virulence factor does streptococcus pyogenes have?
VF prmotes connective tissue breakdown and invasion
what can streptococcus pygenes cause
strep. pyogenes syndromes - streptococcal sore throat, erysipelas (large raised red patches on the skin), necrotising fasciitis, scarlet fever
