Microbiota of the GIT

Question 1

Describe transit time in relation to section of GIT

Answer 1

Transit time gets longer from mouth to large intestine
In large intestine for 10hrs to several days
Stomach 2-4hrs and small intestine 3-5hrs

Question 2

How does transit time affect the microbiota?

Answer 2

Bacterial population effected due to different bacterial growth rates
Also intestinal cell exposure to toxins

Question 3

Describe the bacterial populations along the GIT

Answer 3

Increasing anaerobic conditions
Increasing bacteria density
Increasing dominance of obligate anaerobes

Question 4

What is the total number of bacteria in the human gut?

Answer 4

Up to 100 trillion
Everyone’s microbia is different - unique

Question 5

Why is there a dominant bacteria change along the GIT?

Answer 5

Different oxygen conc., different pH and different transit times

Question 6

What are the pH changes of the GIT?

Answer 6

Mouth - 6.5-7.5
Stomach - 1.5-4
Duodenum - 7-8.5
Ileum - 4-7
Large Colon - 5.5-6.5

Question 7

Why does microbial composition change throughout life?

Answer 7

Anatomy is the same but food is different
Our food is microbiota’s food

Question 8

What is the role of the GIT microbiota?

Answer 8

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

Question 9

What does healthy gut microbiota equal?

Answer 9

Healthy person

Question 10

Is junk food good for microbes?

Answer 10

Junk food provides a lot of calories but does not feed gut microbes as does not reach large colon
Most absorbed in small intestine/stomach - 70% energy uptake

Question 11

What food does GIT microbes grow on?

Answer 11

Fibre - fruit, veg, pulses and whole grains
Converts to different products
Energy absorbed in large intestine

Question 12

What are the benefits of including dietary fibre in our diet?

Answer 12

Improves faecal bulking, eases passage and results in shorter transit time
Contains phytochemicals, antioxidants and vitamins
Bacterial fermentation

Question 13

What does bacterial fermentation do?

Answer 13

Releases additional phytochemicals
Maintains slightly acidic pH
Increased commensal bacterial population
Essential supply of short chain fatty acids

Question 14

What is the right side of the colon responsible for?

Answer 14

Site of most bacterial fermentation
Carbohydrate metabolism
Gives SCFA and gases

Question 14

What does a diverse balanced diet do microbes?

Answer 14

A diverse balanced microbiota and diverse balanced products
What we eat affects amount and type of microbial metabolites produced

Question 14

What does SCFA give?

Answer 14

Acetate, propionate and butyrate

Question 15

What is the left side of the colon responsible for?

Answer 15

Site of most intestinal disease
Protein metabolism
Major products
Branched SCFA, gases, phenols, indoles and amines

Question 16

What are the 3 main short chain fatty acids?

Answer 16

Butyrate, propionate and acetate

Question 17

What is the function of butryrate?

Answer 17

Epithelial cell growth and regeneration

Question 18

What is the function of propionate?

Answer 18

Gluconeogenesis in the liver
Satiety signalling

Question 19

What is the function of acetate?

Answer 19

Transported in blood and to peripheral tissues
Lipogenesis

Question 20

What does pH lowering help?

Answer 20

Pathogen inhibition
Increased Ca absorption

Question 21

What is the optimum pH for growth of pathogens?

Answer 21

Over 6

Question 22

Describe pH and proximal colon

Answer 22

Low pH so pathogen exclusion - Less disease
Quicker transit
High epithelium turnover
High fermentation rates
High SCFA production

Question 23

Describe pH and distal colon

Answer 23

Higher pH - less pathogen exclusion and more protein fermentation - more disease Low substrate concentrations Slower transit so higher exposure to harmful compounds

Question 24

What are the 2 defences which help colonisation resistance?

Answer 24

Barrier effect Active competitive exclusion

Question 25

What is barrier effect?

Answer 25

Large numbers of indigenous microbiota prevent colonisation by ingested pathogen and inhibit overgrowth of pathogenic bacteria This bacteria could be normally at low levels

Question 26

What is active competitive exclusion?

Answer 26

Both microbe to microbe and microbe to host interactions

Question 27

What happens to the products of the bacteria?

Answer 27

transported in blood to liver, peripheral tissues, brain and signalling molecules

Question 28

Why are short chain fatty acids important?

Answer 28

Important signalling molecules

Question 29

How are SCFA detected?

Answer 29

By receptors which secrete gut hormones

Question 30

What are the GPR43/FFAR2 receptors activated by?

Answer 30

Acetate, propionate more than butyrate

Question 31

What are GPR41/FFAR3 receptors activated by?

Answer 31

Propionate and butyrate

Question 32

What are GPR109A receptors activated by and what do they do?

Answer 32

Butyrate Suppress colonic inflammation and carcinogenesis

Question 33

Describe gut microbiota in the development of he immune system

Answer 33

Commensal bacteria close to epithelium block adhesion by pathogens Inner mucus layer prevents bacterial penetration Immune system deals with few bacteria cells leaving epithelium

Question 34

Are microbiota species pro or anti-inflammatory?

Answer 34

Can be either

Question 35

What does bacterial composition and metabolite conc. also effect?

Answer 35

Gut-brain axis

Question 36

What are some non-gut conditions associated with changing of gut microbiota?

Answer 36

CNS - Multiple sclerosis GI - IBD, IBS Metabolism - Insulin resistance, obesity Immunity - allergies, autoimmune disease

Question 37

What are the 2 diseases in inflammatory bowel disease?

Answer 37

Chron's Disease and Ulcerative Colitis

Question 38

What can dysregulation of immune response lead to?

Answer 38

Chronic gut inflammation Autoimmune disease

Question 39

What does inflammation in IBD likely result from?

Answer 39

Dysregulated host immune response to gut microbiota

Question 40

What do CD patients have a lower number of?

Answer 40

F. prausnitizil - anti-inflammatory bacteria Instead an increase in pro-inflammatory

Question 41

What is the effect of antibiotic use and gut microbiota?

Answer 41

Reduces bacterial diversity and increases enterobacteria

Question 42

Explain the vicious cycle in IBD

Answer 42

Decrease in mucus barrier then increase in O2 pressure Then alters microbial composition Which increases inflammation then continues again

Question 43

What are some causes for change in gut microbial composition?

Answer 43

Antibiotic use Inflammation Diarrhoea - decreased transit time Host diet - less fibre Host genotype

Question 44

What decreases diversity of bacteria when antibiotics used?

Answer 44

Selective pressure There is increase in resistant community Gradual recovery but never bac to normal

Question 45

What antibiotics have more effect on intestinal microbiota?

Answer 45

Vancomycin > clindamycin > ciprofloxacin

Question 46

What are the consequences of exposure to antibiotics?

Answer 46

Decreased microbial diversity Opportunity fir pathogen colonisation so results in pathogen dominant community Can end up with recurrent C. difficile infections

Question 47

What can reduce incidence of CDAD?

Answer 47

Probiotics

Question 48

Explain a FMT

Answer 48

Faecal sample from screened healthy donor transplants into patient This displaces C. difficile and prevents reinfection

Question 49

What are the factors which affect gut microbiota?

Answer 49

Environment, diet, life stage, antibiotics, prebiotics, faecal transplant, disease

Question 50

How does decreased dietary carbohydrate content effect faecal short chain fatty acid production?

Answer 50

Decreased production of SCFA Significant decrease un numbers of E.rectale group

Question 51

What are probiotics?

Answer 51

Live microorganisms that when administered in adequate amounts, confer health benefit on host

Question 52

What are prebiotics?

Answer 52

Substrate that is selectively utilised by host microorganisms conferring health benefit Prebiotics are food for resident bacteria

Question 53

What are some widespread mechanisms carried out by prebiotics?

Answer 53

Competition Competitive exclusion Barrier function Reduce inflammation

Question 54

What are some frequent mechanisms carried out by prebiotics?

Answer 54

Bioconversions Direct antagonism Immune stimulation

Question 55

How does prebiotics help satiety signalling?

Answer 55

Stimulate SCFA production by gut microbiota Interact directly with immune cell receptors

Question 56

What are the systemic effects of prebiotics?

Answer 56

Increased health benefit as metabolic effects, satiety an immunomodulatory effects There is decreased inflammation