106 - Gut Microbiota

Question 1

Proportion of faeces that is bacteria

Answer 1

~30%

Question 2

Type of organism that makes up the majority of GIT microbiome

Answer 2

Anaerobic bacteria

Question 3

Main phyla of GIT bacteria

Answer 3

Bacteroidetes, Firmicutes, Actinobacteria, Proteobactiera (relatively rare, EG: E coli)

Question 4

Similarity of microbiota between twins

Answer 4

Under 50% bacterial species shared

Question 5

Processes that genes from microbiota are important for 
1
2
3
4

Answer 5

1) Metabolism
2) Development
3) Immune system
4) Protection against enteropathogens

Question 6

How can the microbiome aid in development?

Answer 6

Intestinal epithelial cell maturation, angiogenesis, lymphocyte development

Question 7

Factors influencing GIT microbiota
1
2
3
4
5

Answer 7

1) Mode of birth
2) Age
3) Diet
4) Antibiotics
5) Genetics and environment
6) Chronic inflammation

Question 8

How can mode of birth affect microbiome?

Answer 8

Vaginal delivery associated with rapid acquisition of Firmicutes, Bifidobacteria.
C-section associated with delayed microbiome development, reduced diversity

Question 9

How can age affect GIT microbiome?

Answer 9

Diversity increases with age

Question 10

How can diet affect GIT microbiome?

Answer 10

Breast milk, low fat/fibre-rich, high fat/high sugar all can affect microbiome

Question 11

Effect of animal-based diets on microbiome

Answer 11

Increases levels of bile-tolerant bacteria (Bacteroides), decreases levels of bacteria that metabolise dietary plant polysaccharides

Question 12

Two theories explaining why germ-free mice need higher calorie diet to maintain body weight
1
2 i, ii

Answer 12

1. The microbiota directly supply nutrients from dietary
   substances, (eg vitamin B2, vitamin K, biotin, folate,
   CHO from plant sugars – 10% calories)
2. The microbiota alter metabolic machinery of host cells by:
   i) inducing changes in host genes involved in CHO and
   lipid metabolism, and
   ii) maintaining enterocyte
   differentiation and function (short chain fatty acids,
   SCFA’s)

Question 13

How do GIT microbiota have a similar effect between individuals, even if the species distribution varies?

Answer 13

Metabolic pathways remain stable between individuals in a healthy population (calculated by examining 16s rRNA ofgut microbiota)

Question 14

Gut microbiota metabolism of carbohydrates

Answer 14

Lactose, cellulose, mucins broken down into SCFA

Question 15

How can gut microbiota lead to synthesis of mucus?

Answer 15

Bacterial degradation of host glycans (mucin, chondroitin, sulphate, etc) elicits synthesis of new glycans by host

Question 16

How can gut microbiota promote gut wall integrity?

Answer 16

Produce short chain fatty acids from undigestible
carbohydrates (eg butyrate) that maintain enterocyte
differentiation

Question 17

How can bacteria contribute to adiposity?
1
2

Answer 17

1) Complex carbs metabolised to SCFA (acetate, propionate, butyrate)
2) SCFA inhibit histone deacetylase, and metabolic regulation through binding to GPCR.

Question 18

Where are Peyer’s patches located?

Answer 18

Small intestine

Question 19

Where in vili do lymphocytes often sit?

Answer 19

Lamina propria, intraepithelial lymphocytes

Question 20

Intraepithelial lymphocytes

Answer 20

Gamma/delta T lymphocytes, sit in the gut epithelium

Question 21

Cells within the GIT that release IL-22

Answer 21

NK cells (NK-22)

Question 22

Role of IL-22 in the gut

Answer 22

Increase antimicrobial defence, epithelial repair, barrier integrity

Question 23

Cell subtype that invariant lymphoid cells resemble

Answer 23

Th17

Question 24

What do mucosal associated invariant T cells detect?

Answer 24

Not completely understood.

Respond to bacterial antigens (EG: riboflavin) presented on an MHC-I-like molecule (are mostly CD8+)

Question 25

NKT cell receptor

Answer 25

CD1d, presenting lipid antigen

Question 26

Ways in which DCs in the GIT can sample antigen

Answer 26

1) Directly from gut lumen

2) Indirectly, delivered by goblet cells or M cells

Question 27

Functions of gut DCs
1
2
3
4

Answer 27

1) In steady state, induce Treg (TGFb), Th2 (anti-inflammatory environment)
2) In inflammatory conditions, induce Th1, Th17
3) Bias B cell isotype switching to IgA
4) Induce mucosal addressin alpha4beta7 on activated T and B cells and receptors for mucosal chemokines

Question 28

alpha4beta7 ligand

Answer 28

MAdCAM1 (only expressed on HEV, epithelial cells of mucosal tissues)