Microbiota of the GI tract

Question 1

What is the transit time in the mouth?

Answer 1

Up to 1 minute

Question 2

What is the transit time in the oesophagus?

Answer 2

4-8 seconds

Question 3

What is the transit time in the stomach?

Answer 3

2-4 hours

Question 4

What is the transit time in the small intestine?

Answer 4

3-5 hours

Question 5

What is the transit time in the colon?

Answer 5

10 hours to several days

Question 6

What does transit time affect?

Answer 6

Bacterial populations

Cell exposure to toxins

Question 7

What increases moving don the GI tract?

Answer 7

Anaerobic conditions
Bacterial density
Dominance of obligate anaerobes

Question 8

What is the most bacterial dense site of the GI tract?

Answer 8

Large intestine

Question 9

What is the predominant colonisation of the large intestine?

Answer 9

Anarobes

Question 10

What are facultative anaerobes?

Answer 10

Can grow in presence or absence or oxygen

Question 11

What are obligate anaerobes?

Answer 11

Cannot grow in the presence of oxygen

Question 12

What factors affect the dominant bacteria at each site?

Answer 12

pH
Transit time
O2 concentration

Question 13

What is the pH of the mouth?

Answer 13

Neutral

Question 14

What is the pH of the stomach?

Answer 14

Acidic

1.5-4

Question 15

What is the pH of the duodenum?

Answer 15

Neutral

7-8.5

Question 16

What is the pH of the ileum?

Answer 16

Acidic

4-7

Question 17

What is the pH of the colon?

Answer 17

5.5-6.5

Question 18

What is the role of the GI microbiota?

Answer 18

Metabolism of dietary components
Production of essential metabolites
Development of immune system
Host signalling
Defence against pathogens
Modifications of host secretions

Question 19

How does the GI microbiota metabolise dietary components?

Answer 19

Microbes grow on fibre and convert it to other products

Question 20

What are the benefits of including fibre in the diet?

Answer 20

Improves faecal bulking

Contains important phytochemical, antioxidants and vitamins

Question 21

What is the purpose of bacterial fermentation of fibre?

Answer 21

Release additional phytochemicals
Maintains slightly acidic pH
Increases commensal bacterial population and resistance to pathogens
Essential supply of short chain fatty acids

Question 22

What short chain fatty acids does fibre supply and what is their purpose?

Answer 22

Butyrate- epithelial cell growth and regeneration
Propionate- gluconeogenesis and satiety signalling
Acetate- lipogenesis

Question 23

How do resident bacteria protect against pathogens?

Answer 23

Lower pH
Create physical barrier
Prime immune system
Produce active components to ‘kill’ incoming pathogens

Question 24

What is the barrier effect?

Answer 24

Large number of indigenous microbiota prevent colonisation by ingested pathogens and inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels

Question 25

What is the gut mucosal immune system?

Answer 25

Mucous layer of the gut forms barrier between lumen bacteria and epithelial cells

Question 26

When do autoimmune disease of the gut occur?

Answer 26

When immune system can no longer distinguish between harmful pathogens and commensal bacteria

Question 27

How does the breakdown of fibre help with signalling?

Answer 27

Short chain fatty acids produced act on receptors on epithelial cells to secrete hormones and have the desired effect

Question 28

What factors influence gut microbiota>

Answer 28

Dietary changes- greatest influence Age Alcohol intake

Question 29

What is changes in microbiota composition associated with?

Answer 29

Disease | This does not mean this is necessarily the cause

Question 30

How might diseases be cause by indigenous microbiota?

Answer 30

Overgrowth Colonisation at a different body site General dysbiosis

Question 31

What is inflammation in IBD likely caused by?

Answer 31

Dysregulated immune response to microbiota

Question 32

What microbiota changes are present in IBD?

Answer 32

Reduced bacterial diversity Reduced stability in bacterial composition Increased mucosal barrier load

Question 33

What is the treatment of IBD?

Answer 33

Broad spectrum antibiotics | Faecal stream diversion

Question 34

Why is it difficult to distinguish between the cause and effect of IBD?

Answer 34

Reduced bacterial diversity could be caused by inflammation or antibiotics

Question 35

What are probiotics?

Answer 35

Live microorganisms which, when administered in adequate amounts, confer a health benefit

Question 36

What are the different mechanisms of action of probiotics?

Answer 36

``` Competition Bioconversion Production of vitamins Direct antagonism Competitive exclusion Barrier function Reduce inflammation Immune stimulation ```

Question 37

What are probiotics?

Answer 37

Selectively fermented food/ingredient that results in specific changes in composition and/or activity of GI microbiota, conferring health benefit on the host

Question 38

What is the effect of antibiotics on microbiota?

Answer 38

Kill pathogen but also commensal bacteria

Question 39

What are the consequences of antibiotic therapy?

Answer 39

Decreased microbial diversity | Opportunity for pathogen colonisation and pathogen dominant community

Question 40

What happens with C. diff post antibiotic therapy?

Answer 40

C. diff expands to occupy empty niches | Overgrowth causes toxin production, fever, abdomen pain, C. diff associated diarrhoea

Question 41

What is the initial treatment of C. diff infection?

Answer 41

Antibiotic therapy

Question 42

What is the treatment for recurring C. diff infections?

Answer 42

Faecal microbial transplant