12.10-12.11

Question 1

Definition of dysbiosis

Answer 1

Changes in normal microbiota, associated with disease.

Question 2

Normal microbiota of healthy humans in gut is mostly Gram ___ organisms and in skin/throat is mostly Gram ___ organisms

Answer 2

Gram NEGATIVES in gut.

Gram POSITIVES in skin/throat.

Question 3

4 major phyla of microbiota:

Answer 3

Bacteroidetes
Firmicutes
Actinobacteria
Proteobacteria

Question 4

Distribution of bacteria in gut is variable e.g. there is ___ bacteria in colon c.f. stomach.

Answer 4

More

Question 5

Can all microbiota be cultured?

Answer 5

No!

Question 6

In the colon, there are more ___ and ___ (phyla) and in skin there are more ___ (phyla).

Answer 6

In colon - Firmicutes and Bacteroides

In skin - more Actinobacteria

Question 7

In a host, is microbiota stable or changing?

Answer 7

Stable!

Question 8

Vaginal delivery is associated with rapid acquisition of ___ (phylum).

Answer 8

Firmicutes (bifidobacteria)

So caesarean delivery can affect microbiota development!

Question 9

What factors influence gut microbiota?

Answer 9

Mode of birth/delivery.
Age
Diet e.g. high fat/low fibre to low fat/high fibre, oral iron intake.
Antibiotics
Genetics/environment
Chronic inflammation e.g. ulcerative colitis, IBD

Question 10

An iron free diet in mice leads to an increase in ___/___ and a decrease in ___

Answer 10

Increase in Bifidobacteria/Clostridia

Decrease in Bacteroides

Question 11

In germ free mice, they need higher energy intake to maintain body weight. Why? (2 reasons)

Answer 11

1 - Microbiota directly supply nutrients from dietary substances (up to 10% of total calories)
2 - microbiota change metabolic machinery of host cells e..g induce changes in host genes for metabolism, and maintain enterocyte differentiation and function (by short chain fatty acids)

Question 12

Are metabolic pathways stable or unstable across sites in a healthy population?

Answer 12

Stable!

But microbiota in different sites in different people can be different!

Question 13

Complex carbohydrates like dietary fibre are metabolised by colonic microbiota to ___ and ___

Answer 13

Oligosaccharides and monosaccharides

Question 14

Oligo- and monosaccharides are fermented to ___ ___ ___ ___ end products

Answer 14

Short chain fatty acid end products e.g. acetate, propionate, butyrate.

Question 15

Butyrate is an important energy source for colonic ___ cells

Answer 15

Epithelial cells

Question 16

Acetate and propionate are substrates for ___ and ___

Answer 16

Gluconeogenesis and lipogenesis in liver and peripheral organs

Question 17

SCFAs can control ___ expression by inhibiting ___, or regulate metabolism by signalling via GPCRs e.g. ___ or ___

Answer 17

Gene expression
Inhibiting histone deacetylase (HDAC)
GPCRs GPR41 or GPR43

Question 18

The gut immune systems is part of ___-___ ___ ___

Answer 18

MALT

Question 19

MALT includes:

Answer 19

Lymphoid tissue from resp. tract, urogenital tract and gut,

Question 20

Aggregates of lymphoid cells in the gut include: ___ ____ ___ and ___ ___

Answer 20

Isolated lymphoid follicles (ILFs) (small AND large intestine)
Peyer’s patches (small intestine ONLY)

Question 21

Lymph nodes associated with small and large intestine are

Answer 21

Mesenteric lymph nodes

Question 22

Lymphocytes are found in the ___ ___

Answer 22

Lamina propria

Question 23

Paneth cells in crypts of GI tissues secrete ___

Answer 23

Defensins - antimicrobial peptides

Question 24

Between enterocytes are ___ ___ ___ (immune cells)

Answer 24

Intraepithelial lymphocytes (IELs)

Question 25

Enterocytes and IELs play an important role in induction of tolerance e.g. due to secretion of ___, and release of the cytokine ___

Answer 25

Defensins from enterocytes/Paneths

TGFbeta from IELs

Question 26

There are different populations of innate lymphoid cells in gut including:

Answer 26

Lymphoid tissue inducer cells (LTIs)
IELs
NK-22 cells (produce cytokines e.g. IL-22 that increas antimicrobial deference, epithelial repair and barrier integrity)
Mucosal associated invariant T cells (MAITs) - respond to riboflavin metabolites.
Invariant NKT cells
Macrophages

Question 27

The ___ cell is located directly over sites of organised lymphoid aggregates, between epithelial cells and ___ antigens to these aggregates

Answer 27

M cell or microfold cell
Delivers antigens
NO MHC so NO presentation, but deliver!

Question 28

Dendritic cells in mucosa can sample antigen from intestinal mucosa ___ or ___

Answer 28

Directly or indirectly

Question 29

In the steady state, DCs in mucosa induce ___ (by cytokine ____, and ___ cells.

Answer 29

Tregs by TGFbeta

and Th2

Question 30

Th2 type cells in the gut help B cells to isotype switch to ___

Answer 30

IgA

Question 31

In inflammation c.f. steady state, when DCs are activated by PRRs, they can induce ___ and ___ responses

Answer 31

Th1 and Th17

Question 32

DCs in mucosa bias isotype switching to secretory ___

Answer 32

IgA

Question 33

DCs in mucosa induce expression of homing receptors on T cells and B cells e.g.:

Answer 33

Induce mucosa addressin a4b7 on activated T cells and B cells.
a4b7 binds to endothelial integrin MAdCAM1

Question 34

Endothelial MAdCAM1 is a ligand for ___

Answer 34

a4b7 addressin

Question 35

Activated T and B cells express chemokine receptor ___ that is specific for lamina propria chemokine ___ on epithelial cells of small intestine ONLY

Answer 35

Chemokine receptor CCR9

Chemokine CCL25

Question 36

What effects do microbiota have on mucus layer and gut epithelium?

Answer 36

Direct effects - block binding sites on epithelial cells. produce bacteriocins to create niche for survival (that can affect pathogens).
Indirect effects - interaction with PRRs, proliferation/stim. of crypt Paneths for defensins, induction of reg. cytokines e.g. TGFbeta.
SCFAs inhibit inflammation (e.g. by NFkB)

Question 37

Peyer’s patches and mesenteric LNs develop ___ (LTi cells), BUT isolated lymphoid follicles (ILFs) develop ___

Answer 37

Prenatally

Postnatally

Question 38

How does the gut epithelium and lymphoid tissue differentiate between normal microbiota and pathogen?

Answer 38

Epithelial PRRs can sense numbers of bacteria and proximity to surface
Epithelial PRRs detect invasion and damage (e.g. TLR5 at basolateral surface for flagellin)
Differential interaction with PRRs

Question 39

If there is inflammation, DCs can bias B cells to produce ___

Answer 39

IgG!

Question 40

Kwashiorkor microbiota generated chemical products that result in selective inhibition of ___-___ ___ ___ enzymes

Answer 40

Tri-carboxylic acid cycle -> effects on energy metabolism for children on a Malawian diet

Question 41

Salmonella typically targets ___ to invade

Answer 41

M cells over Peyer’s patches!

Question 42

Pseudomembranous colitis is due to overgrowth of ___ ___, which adheres to mucosal epithelium and produces a cyto___ toxin that causes cell death, inflammation and bowel necrosis

Answer 42

Clostridium difficle

Cytotoxic

Question 43

Treatment of pseudomembranous colitis with:

Answer 43

Metronidazole +/- vancomycin