GI tract infections

Question 1

How many bacteria in the colon per gram of faeces?

Answer 1

1 billion

Question 2

What does the faecel flora have the metabolic capacity of?

Answer 2

The liver

Question 3

Bacteria in the GI tract

Answer 3

Obligate anaerobes such as bacterioides outnumber facultative bacteria by 100:1

Question 4

Bacterial roles in the GI tract

Answer 4

Synthesising vit k and B12

Digesting tryptophan as a neuroprotectant

Question 5

How many cases of diarrhoeal disease per year?

Answer 5

1.7 billion

Question 6

Bacterial causes of diarrhoeal disease

Answer 6

• Salmonella
• Shigella
• Bacillus cereus
• E.coli
• Campylobacter
• Staph
• Clos difficile
• Vibrio cholerae

Question 7

Bacteria that adhere

Answer 7

• E.coli
• Shigella sonnei
• Campylobacter
• Salmonella

Question 8

Cholera

Answer 8

• Vibrio cholerae
• Rice water stool
• Spread by faecel oral route
• Kills 95,000 people a year
• We have an oral vaccine and oral rehydration

Question 9

Cholera toxin

Answer 9

• cholera toxin has 2 subunits (a and b)
• alpha subunit ribosylates G proteins so cAMP is ribosylated
• b subunit binds to the gangliosides and is translocated into the cell

Question 10

What do S. enterica, S. enteritidis and S. typhimurium contaminate?

Answer 10

Poultry; egg layers vaccinated in 1993

Question 11

Entry of salmonella into the cells?

Answer 11

Via bacterial mediated endocytosis and the whole bacteria moves via the tight junction which disrupts it .
They can target macrophages

Question 12

Which bacteria has a type III secretion system? What does this do?

Answer 12

Salmonella enterica
Injects effector molecules from the bacterial cytosol to the eukaryotic cytosol.
activates GTPases Rho and Rac which leads to the binding up of the membrane so lysozomes can’t fuse

Question 13

E.coli O157

Answer 13

Enterohaemorragic and has a shiga like toxin via pathogen island

Question 14

C. difficile infections

Answer 14

Toxin mediated
Toxin A and B are 300kDa in size
Can colonise after antibiotic use and disrupt the membrane leading to pseudomembrane collitis, diarrhoea and toxic megacolon
Toxin A and B are very similar to human proteins so can be internalised by the receptor. Acidification activates the toxin and it moves outside the vacuole. Rho and Rac modification causes cell death and tight junction disruption.

Question 15

What does campylobacter cause?

Answer 15

• Food poisoning
• Reactive arthritis
• Guillan-Barres syndrome
• IBS

Question 16

Where is campylobacter obtained from?

Answer 16

Uncooked meat, unpasteurised milk and untreated water

Question 17

Campylobacter mechanism of action

Answer 17

Proteins on the surface of campylobacter are similar to those on neurons so neurons can be targeted.
Can arrest cell cycle division at the G2 phase.

Question 18

Treating gastroenteritis

Answer 18

Antibiotics are only used in the very young, very old or in a campylobacter infection