Pathogens and Host Flashcards
A clinical infection is characterised by which signs and symptoms? (7)
- inflammation
- pain
- pyrexia (fever)
- rigors
- increased WBC count
- increase C reactive protein
- tachycardia
what is an acute illness/symptoms? examples?
sudden and severe in onset such as asthma or a broken bone
what is a latent infection?
infection which is dormant (“sleeping”) and may reappear if activated
what is a sub-clinical infection?
asymptomatic infections with no signs or symptoms
what is definition of pathogen?
organism which can cause disease
what is definition of commensal? what is an example?
organism which is part of the normal flora (e.g. e.coli in the gut or s.aureus in the nose or axilla
which patients particularly make it difficult to distinguish between a pathogen and a commensal?
immunosuppressant patients
what is meant by Koch’s Postulates?
criteria established by Koch to identify the causative agent of a particular disease
what are the 3 Koch’s postulates? (criteria)
- organisms must be found in all cases of the disease
- able to be cultured outside the body for several generations
- should reproduce the disease on inoculation
what are the 4 things which should be known when identifying the causative agent of a particular disease?
Knowledge of…
- sterile/non-sterile sites
- normal flora of site
- organism’s pathogenicity
- clinical context
what does host-pathogen interaction depend on?
Patient’s immune system (e.g. pregnant, chronic condition or acute illness all have different immune systems)
what is meant by pathogenicity?
the capacity of a micro-organism to cause an infection
what are 2 requirements for pathogenicity?
- virulence
2. infectivity
what does virulence mean?
ability to cause harmful effects once pathogen is established
what does infectivity mean?
- ability for pathogen to become established
what are 2 examples of infectivity mechanisms?
- attachment (e.coli)
2. acid resistance (helicobacter pylori)
what are the 3 virulence factors which are microbial components?
- invasiveness
- toxin production
- evasion of the immune system
what is meant by invasiveness?
how fast the pathogen takes over the body
what are 3 types of toxins?
- exotoxin
- enterotoxin
- endotoxin
what is an exotoxin?
released extracellularly by the micro-organism
what is an enterotoxin?
they are exotoxins which act on the GI tract
what are endotoxins?
structurally part of the gram negative cell wall (intracellularly) , released from bacteria cell wall
what is an example of an exotoxin?
tetanus:
- infection of dirty wounds
- binds to nerve synapses and loss of inhibitory neurotransmitter
- death caused by respiratory paralysis
what is an example of an enterotoxin?
cholera;
- food and water contamination
- colonises small intestine
- increases cAMP, inhibits uptake of Na and CL, stimualtes secretion of Cl and HCO3 and outflow of H2O
- death by dehydration
where are superantigens found?
in certain exotoxins of strep. pyogenes and staph. aureus
what do superantigens do?
- stimulate division of t cells at the ABSENCE of specific antigens
- overwhelming cytokine production is activated causing toxic shock
- t cells are not specific to particular antigens and cause a huge immune response
what is an example of an endotoxin?
- e.coli ( and other gram negative bacilli)
- neisseria meningitidis (induces cytokines production)
what part of the endotoxin can lead to septic shock?
the lipid component (lipid A) , it’s toxic
what are the harmful effects caused by? (3)
- bacterium
- the host response
- both
