Mechanisms of bacterial pathogenesis I Flashcards
Describe the process of balanced pathogenicity
Balance between pathogenic and defensive mechanisms
Properties of the microbe:
- Adhesins
- Toxins
- Capsule
- Enzymes
Properties of the host
- Natural barriers
- Defensive cells
- Complement
- Immune response
What are the 4 types of infection?
1) Local - surface infection
e.g. V.cholera; N. gonorrhoeae
2) Invasive - penetrate barrier spread, wound
Shigella; Staph aureus
3) Systemic - via blood, lymph to other sites
S.typhi, N. meningitidis
4) Immunopathology - inflammation, cross reactive antigens, granuloma
Outline the stages of infection
1) Acquisition
2) Colonisation - adherence
3) Penetration
4) Multiplication and spread
5) Immune evasion
6) Damage
7) Transmission - shedding
8) Resolution
List 6 examples of bacterial virulence determinants
1) Adherence factors - fimbriae (pili) adhere to cells
2) Invasion factors: surface components and secreted effector proteins
3) Capsules: polysaccharides - protect from opsonisation and phagocytosis
4) Endotoxins: lipopolysaccharide on Gram-negatives - cause fever, changes in BP, inflammation, lethal shock
5) Exotoxins: protein toxins and enzymes produced/ secreted (e.g. cytotoxins, neurotoxins and enterotoxins)
6) Siderophores: iron binding factors to compete with the host for iron haemoglobin, transferrin and lactoferrin
Outline the pathogenesis of 6 important bacteria
Bordetella pertussis (whopping cough)
– toxins and non
- invasive
Vibrio cholera
– non-invasive enteritis
Neisseria. meningitidis
– nasopharynx carriage then express virulence factors = meningitis and septicaemia
Staph. aureus
– locally invasive and toxins
Myobacterium tuberculosis
– invasive, immunopathology and granuloma
Strep. pneumoniae
– inflammatory: teichoic acid, damage via toxins, carriage and invasion
- How does the M protein of streptococcus pyogenes act as an adhension factor of the bacterium?
- this hypervariable adhesion tips allow the adherence to the host
- How does the fimbriae of Neisseria gonorrhoeae allow the bacterium to adhere to uroepithelial cells?
- firstly the fimbriae adhere weakly to uroepethelial cells
- but it brings bacterium closer to the surface so then adhesion molecules on surface of N. gonorrhoeae can form a stronger attachment
What are the 4 functions of bacterial toxins in infection?
1) Promote adhesion, survival or spread of bacteria
2) Damage or destroy cells
3) Interfere with cell metabolism
4) Affect nerves
Outline the 4 types of toxins and give examples of associated infections?
Type I – at cell membrane - not transported in (e.g. travellers diiarrhoea, toxic shock syndrome, scarlet fever)
Type II – on cell membrane - membrane damage (e.g. Clostridium perfingens, Necrotising fasciitis)
Type III – intracellular effect after translocation (e.g. dysentery, diphtheria)
Extracellular – cellular matrix or connective
tissue
What are 2 ways that type III toxins are classified?
Classified by:
1) Enzymatic action
2) Molecular target or effect
Define Koch’s postulates
Four criteria to determine causative relationship
between microbe and disease:
1) Be present in every case of infection
2) Be cultured from cases in vitro
3) Reproduce disease in an animal
4) Be isolated from the infected animal
What are neurotoxins and give examples?
Tetanus - muscle spasms due to blocking GABA receptors and only stimulating motor neurones
–>spastic paralysis
Botulism (floppy baby syndrome) - blocks release of ACH from vesicles, prevents muscle contraction
–> Flaccid paralysis
