10. Micro-organisms in Disease Flashcards
what is pathogenicity?
the capacity of a micro-organism to cause an infection
what are the characteristics of a pathogenic organism?
transmissibility
establishment in or on a host
harmful effects
persistence
what is virulence?
the degree to which a micro-organism is able to cause disease. allows a relative description of pathogenic potential
what is LD50?
dose of an organism that all cause death in 50% of the animals exposed to it
what is ID50?
dose of an organism that will cause infection in 50% of the animals exposed to it
what is infectivity?
the ability of a micro-organism to become established on or in a host. either accomplished with the help of a microbial ligand or a host cell surface receptor
what are virulence factors?
components of micro-organisms that result in harmful effects
what are virulence mechanisms of micro-organisms?
facilitation of adhesion (adhesins)
toxic effects (toxins)
tissue damage (aggressins)
interference with host defence mechanisms (interferins)
facilitation of invasion
modulation of the host cytokine responses (modulins)
when are endotoxins released?
damaged to dead bacterial cells
what is the active component of an endotoxin?
lipopolysaccharide (LPS)
how does LPS harm the body?
binds to a number of host cell receptors and induces a range of uncontrolled host responses
where are endotoxins found?
bacterial cell wall
what is the effect of exotoxins?
systemic inflammatory response syndrome, involving
- uncontrolled t lymphocyte response
- uncontrolled activation of the clotting cascade
- uncontrolled activation of the complement
what are the effects of an uncontrolled t lymphocyte response?
cytokine release
fever, riggers, hypotension, tachicardia, collapse
cardiac and/or renal failure
what are the effects of uncontrolled activation of the clotting cascade
disseminated intravascular coagulation (DIC)
depletion of clotting factors
bleeding tendency
where are exotoxins food and how can they be tackled?
produced by living bacteria
patients can be treated by actually killing the bacteria
which organism causes botulism?
clostridium botulinum
how does c. botulinum spread?
ingestion of pre-formed toxin
infection of dirty wounds
GI colonisation in infants
what are the effects of botulism?
causes flaccid paralysis because it blocks muscle contraction
what is the clinical presentation of botulism?
diplopia dysphagia dysarthria dry mouth death due to respiratory failure
what organism causes tetanus?
clostridium tetani
what toxin is produced in tetanus?
tetanospasmin
what are the effects of tetanospasmin?
binds to nerve synapse, inhibits release of inhibitory neurotransmitters in the CNS
eventually leads to death due to respiratory paralysis
what are the effects of strep. progenies virulence factors?
promote connective tissue breakdown and aids invasion
what are the syndromes caused by strep. pyogenes?
streptococcal sore throat
erysipelas
necrotising fasciitis
scarlet fever
how does s. pyogenes evade the immune system?
m protein binds to fibrinogen and masks the bacterial surface, blocking complement binding and opsonisation
how does s. pneumoniae evade the immune system?
its polysaccharide capsule inhibits opsonisation and therefore phagocytosis
which pathogens are intracellular?
mycobacterium tuberculosis
salmonella typhi
listeria monocytogenes
