GI Tract Pathogens Flashcards
(29 cards)
What causes food poisoning?
Bacterial toxins without colonisation of the host
Onset after a few of hours
Give three pathogens that cause food poisoning
- C. botulinum (toxin)
- S. aureus (superantigen)
- C. perfringens (toxin and superantigen)
Where does C. botulinum grow?
Obligate anaerobes
Home-canned foods
Where does S. aureus grow?
Custard, processed meats
Where does C. perfringens grow?
Spores survive in pre-heated foods
Where do the genes for cholera toxin come from?
Bacteriophage integrated into bacterial chromosome
Co-regulated with other adhesin and other genes by HAP
How is cholera spread?
Faeco-oral route
Contaminated water
What is the structure of the cholera toxin?
AB5
How does cholera toxin cause disease?
B binds to GM1-ganglioside and taken up by receptor-mediated endocytosis
Retrograde transport to endoplasmic reticulum
ADP-ribosylates Gs protein, permanently activating it
Uncontrolled high levels of cAMP
Disturbs activity of CFTR Na+/Cl- pumps
Leads to ion imbalance, massive water loss and watery diarrhoea
Where does S. typhi replicate?
In macrophages
How is S. typhi spread?
Systemically through bloodstream to liver and spleen etc
What causes the symptoms of typhoid fever?
- Typhoid toxin
2. Respond to LPS lipid A
How is bacteria shed?
In bile
Returns to intestine and environment
Spread by faeco-oral route
What causes traveller’s diarrhoea?
Enterotoxigenic E. coli (ETEC)
What is the ETEC zoonosis?
Piglet
How does EPEC bind to host cell surface?
- Delivers protein effectors into host cell by needle
- Tir protein, which binds to EPEC surface intimin
- Causes actin polymerisation and pedestal formation
- Forms very tight junction
What is the predominant EHEC serotype?
O157
How does EHEC cause damage?
- Inflammation
- Shiga-like toxin
- Causes renal failure
What causes bacterial dysentery?
Shigella
What are the symptoms of bacterial dystentery?
- Acute inflammation of colon
- Low-volume diarrhoea containing blood, mucus and PMNs
- Damage caused directly by Shiga toxin
What is antibiotic-associated diarrhoea?
- Antibiotics eradicate host gut microflora
- C. difficile colonises gut
- Causes diarrhoea
What toxins does C. difficile secrete?
TcdA and TcdB
Glycosylate small GTPases in intracellular signalling pathways
Causes leaky epithelium
What do faecal transplants treat?
Recurrent C. difficile infections
What is Helicobacter pylori?
Spiral-shaped gram negative bacteria
Causes 90% of gastric and duodenal ulcers
