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BOD > GI Tract Pathogens > Flashcards

GI Tract Pathogens Flashcards

1
Q

What causes food poisoning?

A

Bacterial toxins without colonisation of the host

Onset after a few of hours

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2
Q

Give three pathogens that cause food poisoning

A
  1. C. botulinum (toxin)
  2. S. aureus (superantigen)
  3. C. perfringens (toxin and superantigen)
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3
Q

Where does C. botulinum grow?

A

Obligate anaerobes

Home-canned foods

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4
Q

Where does S. aureus grow?

A

Custard, processed meats

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5
Q

Where does C. perfringens grow?

A

Spores survive in pre-heated foods

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6
Q

Where do the genes for cholera toxin come from?

A

Bacteriophage integrated into bacterial chromosome

Co-regulated with other adhesin and other genes by HAP

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7
Q

How is cholera spread?

A

Faeco-oral route

Contaminated water

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8
Q

What is the structure of the cholera toxin?

A

AB5

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9
Q

How does cholera toxin cause disease?

A

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

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10
Q

Where does S. typhi replicate?

A

In macrophages

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11
Q

How is S. typhi spread?

A

Systemically through bloodstream to liver and spleen etc

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12
Q

What causes the symptoms of typhoid fever?

A
  1. Typhoid toxin

2. Respond to LPS lipid A

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13
Q

How is bacteria shed?

A

In bile

Returns to intestine and environment

Spread by faeco-oral route

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14
Q

What causes traveller’s diarrhoea?

A

Enterotoxigenic E. coli (ETEC)

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15
Q

What is the ETEC zoonosis?

A

Piglet

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16
Q

How does EPEC bind to host cell surface?

A
  1. Delivers protein effectors into host cell by needle
  2. Tir protein, which binds to EPEC surface intimin
  3. Causes actin polymerisation and pedestal formation
  4. Forms very tight junction
17
Q

What is the predominant EHEC serotype?

A

O157

18
Q

How does EHEC cause damage?

A
  1. Inflammation
  2. Shiga-like toxin
  3. Causes renal failure
19
Q

What causes bacterial dysentery?

A

Shigella

20
Q

What are the symptoms of bacterial dystentery?

A
  1. Acute inflammation of colon
  2. Low-volume diarrhoea containing blood, mucus and PMNs
  3. Damage caused directly by Shiga toxin
21
Q

What is antibiotic-associated diarrhoea?

A
  1. Antibiotics eradicate host gut microflora
  2. C. difficile colonises gut
  3. Causes diarrhoea
22
Q

What toxins does C. difficile secrete?

A

TcdA and TcdB

Glycosylate small GTPases in intracellular signalling pathways

Causes leaky epithelium

23
Q

What do faecal transplants treat?

A

Recurrent C. difficile infections

24
Q

What is Helicobacter pylori?

A

Spiral-shaped gram negative bacteria

Causes 90% of gastric and duodenal ulcers

25
Q

Where does H. pylori colonise?

A

Mucin layer near gastric mucosal cells in stomach antrum

26
Q

How does H. pylori colonise gastric epithelium?

A
  1. Motile due to flagellum
  2. Binds cells by adhesins
  3. Neutralises acid by urease
  4. Makes mucus less viscous by mucinase
27
Q

How does H. pylori cause ulceration?

A

Intense mucosal inflammation

  1. Induces IL-8 production by epithelial cells, attracting PMNs
  2. Destruction of epithelial cells by VacA toxin - pore-forming and vacuolating
28
Q

How does the H. pylori VacA toxin cause disease?

A
  1. Inserts into host cell membrane to form anion-selective channels that are endocytosed
  2. Pores disturb ion balance of late endosomes and water flow in
  3. Turns endosomes into vacuoles
29
Q

How might stomach ulcers lead to gastric cancer?

A

Chronic inflammation exposes proliferating stem cells to dietary carcinogens and generates mutagenic ROS

Bacterial effector CagA delivered into gastric epithelial cells leads to increased cell proliferation

BOD (8 decks)

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