GIT pathogens - Bacteria - Non-invasive Flashcards
Types of non-invasive pathogens 1) 2) 3) 4)
1) Vibrio cholerae
2) ETEC
3) EPEC
4) EHEC
Cholera toxin structure
AB5
Cholera toxin receptor
GM1 ganglioside on intestinal cells
Cholera toxin mode of action 1) 2) 3) 4) 5)
1) Locks GTPase into ‘ON’ position.
2) This increases adenylate cyclase concentration.
3) This increases cAMP levels.
4) This inhibits Na+ entry into villous cells.
Increases Cl- expulsion from crypt cells.
5) This leads to osmotic loss of water from cells
Agar used to detect vibrio cholerae
Thiosulphate citrus bile salts sucrose agar (TCBS).
Appearance of vibrio cholerae on TCBS agar
Yellow colonies.
Other vibrio form green colonies.
ETEC infective dose
10^8/g of food.
ETEC toxins
ST, LT.
ST comparison to cholera toxin
Different structure, same effect (change in cell isn’t permanent).
LT comparison to cholera toxin
Same structure, same effect (permanent change in cells).
ETEC pili
Colonisation factor antigen (CFA)
EPEC infectious dose in adults
10^9/g of food
EPEC pathogenic proteins
bfp, tir, intimin (eae gene)
Bfp gene location
EPEC adherence factor plasmid (EAF plasmid)
EHEC transmission
Zoonosis.
From unaffected animal reservoirs to humans via undercooked meat.
EHEC pathogenesis
Type III secretion system (tir, intimin, pedestal formation).
Shiga toxin secretion.
Shiga toxin structure
AB5
Shiga toxin receptor
Gb3 on endothelial cells
Shiga toxin pathogenesis
N-glycosidase.
Removes nucleic acids from ribosomes, prevents function.
Damages vasculature.
Haemolytic uremic syndrome
Gb3 on kidney glomeruli. Bound to by shiga toxin.
Abdominal cramps –> watery diarrhoea –> dysentary.
EHEC agar
Sorbitol-MacConkey agar. Non-soritol fermenting.
EHEC PCR
stx1, stx2, eae (intimin).
Enzyme immunoassay for shiga toxin.
stx1 and stx2.
