3.5 Pathogenesis of infective diarrhoea Flashcards
define intoxication
when a person ingests a toxin that has been produced outside of the body
define infection
results when a pathogen inhabits the body and subsequently causes disease (only occurs when bacteria replicates in the body)
What causes diarrhoea
either an altered movement in ions and water that follows an osmotic gradient
What are the 6 mechanisms causing diarrhoea?
- Increased Cl secretion (CFTR and CLCA)
- Reduced Na absorption (NHE3)
- Increased paracellular permeability
- Reduced Cl absorption (DRA)
- Reduced H2O absorption (aquaporins)
- Reduced Na and glucose absorption (SGLT-1)
What type of pathogen is vibrio cholera?
Gram negative, facultative anerobe, highly motile rod with a single polar flagella
How does vibrio cholera infect people?
infect via the consumption of contaminated water/food
What are the symptoms of vibrio cholera?
Acute watery diarrhoea with severe dehydration
What is the treatment of vibrio cholera?
80% with oral rehydration salts, some may need IV fluids if severely dehydrated
May require antibiotics do diminish duration, reduce volume of rehydration
What factors of vibrio cholera are essential for colonisation?
Pilus TCP (for adhesion) and GbpA
What is the structure of vibrio cholera?
A subunit bound to a pentameric ring of B subunits
What is the role of the B subunits in vibrio cholera?
deliver the A subunit into the cell to cause diarrhoea
What is the function of the cholera toxin?
The A subunit of the cholera toxin causes increased Cl secretion and decreased Na absorption leading to an increase in NaCl levels in the lumen
How does the cholera toxin A sub unit cause diarrhoea?
Activates adenylate cyclase which catalyses the conversion of ATP to cAMP increasing the activity of the chloride transporter and decreasing the activity of Na transporters
What type of pathogen is Enterotoxigentic E.Coli?
Gram negative, facultative anaerobe, motile rod with many flagella
How does Enterotoxigentic E.Coli cause infection?
Causes increased Cl secretion and decreased Na absorption by the heat stable toxin binding to guanylyl cyclase on small intestine epithelium catalysing GTP to cGMP increasing the activity of chloride (CFTR) and decreasing Na (NHE3) transporter
What type of pathogen is Enterohaemorrhagic E.Coli?
Gram negative, facultative anaerobic rod
What are the main sources of EHEC?
raw or undercooked ground meat products, raw milk and fecal contamination of vegetables
What are the symptoms of EHEC?
Diarrhoea or bloody diarrhoea (haemorrhagic colitis/haemorrhagic uraemic syndrome)
Fever
Do you use antibiotics for EHEC?
Not antibiotics because it will increase the risk of haemorrhagic uraemic syndrome
What are the colonisation factors of EHEC?
Intimin and Tir
How does EHEC cause infection?
the Tir receptor on the Intimin binds causing decreased surface area for nutrient absorption, causing increased osmolarity of the intestinal contents and malabsoprtion
How do shiga toxins cause diarrhoea?
toxin A subunit inactivates ribosomes by inhibiting protein synthesis and causes apoptosis. toxin 1 and 2 inhibit absorption of water causing luminal fluid accumulation in the intestine
What kind of pathogen is C. Difficile
Gram positive, spore forming rod
What are the colonisation factors of C.Difficile?
S layer proteins
Cell wall protein
Fbp68
FliC-FliD components of flagella
