Microbiota of the Gut

Question 1

How does transit time through the GI tract affect toxins or bacteria

Answer 1

Longer the transit time, more potential for toxins or detrimental bacteria to interact with human cells

Question 2

What do bacteria become as you progress through the GIT

Answer 2

More anaerobic

• mouth: facultative
• colon: obligate

Question 3

Which part of the GIT has the most variable bacteria and which is the most densely populated

Answer 3

Variable - Mouth

Densely - Large intestine

Question 4

Facultative vs Obligate Anaerobes

Answer 4

F - can grow in the presence and absence of oxygen

O - cannot grow in presence of oxygen

Question 5

6 Functions of gut microbiota

Answer 5

1. Metabolism of dietary components
2. Production of essential metabolites to maintain health
3. Development of immune system
4. Host signalling
5. Defence against pathogens (competition, barrier, pH inhibition)
6. Modification of host secretions (mucin, bile, gut receptors)

Question 6

Where do GIT microbes grow on

Answer 6

Fibre in fruit, veg, pulses and whole grains

Question 7

Benefits of dietary fibre

Answer 7

Health protection (faecal bulking, easing passage, short transit time)
Phytochemicals, anti-oxidants and vitamins
Bacterial fermentation - supplies essential SCFA and maintains acidic pH by releasing acids

Question 8

In what ways do GIT microbes use colonisation resistance to defend against pathogens

Answer 8

1. Barrier Effect: large numbers of indigenous microbiota prevent colonisation by ingested pathogens AND inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels)
2. Active Competitive Exclusion: mucous layer forms barrier between luminal bacterial population and epithelial cells, pH also defends

Question 9

At what pH do pathogens optimally grow at

Answer 9

6

Question 10

Describe the layers of protection of the intestinal epithelium

Answer 10

1. Commensal bacteria close to epithelium block and prevent adhesion or colonisation by pathogens
2. Outer mucous layer barrier effect
3. Inner mucous layer prevents bacterial penetration
4. Few bacterial cells which penetrate dealt with by immune system

Question 11

Which receptors detect penetrating bacteria

Answer 11

Pattern Recognition Receptors
- bind to pathogens and activate signalling cascades

Toll like Receptors
- specifically recognise bacterial components

Question 12

How do the gut microbiota activate host signalling molecules

Answer 12

Their metabolites and products of digestion:

i.e. SCFA can activate receptors on gut epithelial cells

Question 13

What do bacteria in the large intestine do

Answer 13

Ferment dietary fibre - release SCFA

Question 14

How do resident bacteria prevent pathogen colonisation

Answer 14

Lower pH
Create physical barrier
Prime immune system
Produce active compounds which kill incoming pathogens