L1 - How Pathogens cause disease Flashcards
What 3 things do microbes need to survive?
1) find suitable habitat
2) exploit the habitat
3) disperse to new habitat
What are strategies to maximise chance of bacterial survival?
Damage host
Damage/destroy competing bacteria
What are Koch’s postulates?
causative organism isolated from every individual
cultivated in artificially pure culture
inoculated from pure culture - result in typical symptoms
recover from individuals infected experimentally
What are virulence gene postulates?
gene encoding trait present and transcribed in virulent strain
gene encoding NOT present in non-disease causing gene
disruption of gene in virulent strain = form strain incapable of disease
introduction of genes into silent strain = disease causing strain made
What are the problems with Koch’s postulates
- cannot grow organisms
- issue if solely infects humans
- some things do not fit the categorisation
What are endogenous infections?
commensal bacteria getting into the wrong places
What are examples of endogenous infections?
Oral streptococci
endocarditis
Honeymoon cystitis
Pneumococcal pneumonia
Meningococcal meningitis
What are exogenous infections?
Foreign bacteria causes disease
What are examples of exogenous disease
Respiratory - TB
Faecal-oral - shigellosis
Venereal spread - Syphilis
What is horizontal and vertical spread?
horizontal - between humans
vertical - parents infect offspring
What are the 2 types of virus entry
ingress
penetration
What are latrogenic infections?
contaminated blood transfusions - syphillis
What are adhesions involved in?
determining tissue tropisms of bacterial infection
How can bacteria evade defences?
inhibit opsonisation
inhibit chemotaxis
kill phagocyte
inhibit phagocytosis
inhibit lysosomal fusion
…..
What are the ways in which strep pyogenes can evade defences and spread?
capsule
leukocidins
degradation of host tissue:
- hylauronidase
- streptokinase
- streptodornase
- proteases
