The microbiota of the GI tract

Question 1

What is a facultative anaerobic bacteria?

Answer 1

Can grow in the presence of oxygen AND in the absence of oxygen

Question 2

What is a obligate anaerobic bacteria?

Answer 2

Cannot grow in the presence of oxygen

Question 3

How can the gut microbiota act as defence against invading pathogenic bacteria?

Answer 3

o Competition
o Barrier function
o pH inhibition

Question 4

What are the functions of the gut microbiota?

Answer 4

Defence against invading pathogens
Modification of host secretions
Metabolism of host dietary components
Production of essential metabolites for host health
Development of host immune system
Host signalling

Question 5

What are the benefits of inclusion dietary fibre in our diets?

Answer 5

o Improves faecal bulking, eases passage, results in shorter transit time
o Contains important phytochemicals, anti-oxidants and vitamins
o Bacterial fermentation

Question 6

Why is bacterial fermentation important?

Answer 6

• Releases additional phytochemicals
• Maintains slightly acidic pH
• Increased commensal bacterial population and pH improves resistance to pathogens
• Essential supply of short chain fatty acids

Question 7

What are the 3 main short chain fatty acids (SCFAs)?

Answer 7

Butyrate - Epithelial cell growth energy source and regeneration

Propionate - Gluconeogenesis in the liver and satiety signalling

Acetate - Transported in blood to peripheral tissues, lipogenesis

Question 8

What short chain fatty acid is the energy source for epithelial cell growth and regeneration?

Answer 8

Butyrate

Question 9

What short chain fatty acid is used for gluconeogenesis in the liver and for satiety signalling?

Answer 9

Propionate

Question 10

What short chain fatty acid is transported in the blood to peripheral tissues for lipogenesis?

Answer 10

Acetate

Question 11

What is the ratio of the main SCFAs in normal health (butyrate:propionate:acetate)?

Answer 11

1:1:3

Question 12

List some receptors that recognise SCFAs to initiate signalling?

Answer 12

o FFAR2 – activated by acetate, propionate > butyrate, results in GLP-1 secretion (inhibits fat accumulation)
o FFAR3 - activated by propionate and butyrate, results in PYY secretion (improves insulin resistance and satiety signalling to brain)
o GPR109A - activated by butyrate, suppresses colonic inflammation and carcinogenesis (anti-inflammatory cytokines eg. IL-10)

Question 13

What happens when FFAR2 binds SCFAs?

Answer 13

FFAR2 – activated by acetate, propionate > butyrate, results in GLP-1 secretion (inhibits fat accumulation)

Question 14

What happens when FFAR3 binds SCFAs?

Answer 14

FFRA3 activated by propionate and butyrate, results in PYY secretion (improves insulin resistance and satiety signalling to brain)

Question 15

What happens when GPR109A binds SCFAs?

Answer 15

GPR109A - activated by butyrate, suppresses colonic inflammation and carcinogenesis (anti-inflammatory cytokines eg. IL-10)