1.7. The gut microbiome Flashcards
Microbiome
the genes present in all the microorganisms living in association with the host
microbiota
refers to the actual organisms
what bacteria are present?
- Bacteroidetes (e.g. Bacteroides, Prevotella)
- Firmicutes (e.g. Clostridium, Lactobacillus)
- Actinobacteria (e.g. Bifidobacterium)
- Proteobacteria (e.g. Escherichia)
- Fusobacteria
- Cyanobacteria
- Verrucomicrobia (e.g.Akkermansia)
the gut microbiota
- Bacterial load & pH increase throughout gut
2. antimicrobials & oxygen decreases as you progress through GIT
appendix
source of organisms for repopulating large bowl
=> repository/ safe space for organisms
small bowel
=lots of O2
- increases O2 on epithelium
- proteins which inhibit growth of microorganisms:
- IgA –> lumen of gut
- Antimicrobial proteins
* decreases the number of proteins in the small bowl ==> don’t want too many microorganisms in the small bowel –> eat our food
large bowel
= 2 mucus layers
inner and outer layer have different organisms
* organisms breakdown and eat mucus population to survive
describe of the individual GIT microbiota
- begins before we are born
- major colonization –> from vagina
- -> maternal vaginal microbiome change before baby is born and change back after - human breast milk –> nourishes bacteria
- changes when child begins eating adult food
- microbiome stabilizers at 2/3 years
- similar to people we live with –> same microbiota
what factors affect the GIT microbiota?
- diet - controls actual numbers of each species
*more diverse diet = more microbiotas - environment - antibiotics, sanitation, drugs
e.g. PPI - proton-pump inhibitors (treat ulcers etc., but have a negative effect longterm)
(1+2 = responsible for reduction in diversity & dysbiosis) - host immune system is hard to quantify in humans (e.g. IgA deficiency)
what are the roles of microbiota?
- provide enzymes –> makes energy and nutrients available from food that we can’t process
- regulates immunity & metabolism
- produces metabolites –> absorbed –> provide specific signals –> become part of our physiology
- release cell components (e.g. PSA) which also complement our physiology
list the functions of energy and metabolism
- extra energy available because more digestive enzymes are in the gut
- upregulates transporters of CHO & lipid
- influence glucose homeostasis
- affects bile salt metabolism
- affects appetite by altering secretion of gut hormones and increasing leptin sensitivity
Control of the epithelium-microbiota interface
–AMPs:Antimicrobial peptides.
–Goblet cells produce mucus.
–Small intestine mucus layer is impervious to colonisation or bacterial penetration due to high concentrations of AMPs and secretory IgA(sIgA).
–Colon: Outer mucous layer (less dense than inner layer) is highly colonised by specific microbiota.
list the 3 levels of protection Intestinal Microbiota Promote
I.Saturate colonisation sites.
II.Drive mucin production, IgA secretion, AMP expression.
III.Enhance immune responses to invading pathogens.
dysbiosis
- loss of overall diversity
- change in the ratios of major phyla
- bloom of specific bacterium, especially one with the potential to cause damage
* don’t know if change is cause of effect of disease
how does antibiotic treatment affect the individual?
- pathogen susceptibility
- decreases diversity
- decreases dysbiosis
what are some of the effects of dysbiosis?
- immune dysregulation
- obesity
- IBD (inflammatory bowel disease)
how does antibiotic treatment affect the population?
cumulative affect across generations to affect the whole community
Metabolite:
SCFAs
*produced by bacteria from fibre in the diet and act in the gut as well as being absorbed
*SCFA= short chain fatty acid
*main SCFA= acetate, butyrate & propionate
1. produced by bacteria from fibre we absorb and can’t break down in the small intestine –> therefore SCFA produced in the large bowel
2. gluterate = major source of energy for normal colon epithelial cells –> not enough fiber = not enough gluterate ==> not enough energy in colon cells
3. gluterate is also from cheese and butter
4. enhances innate immune system –> goblet cells stimulated to produce more mucous –> supports mucous-loving microbiota & protects surface of epithelial cells from attack by pathogenic bacteria
5. enhances Treg cells in adaptive immune system –> dappens down immune system with product of IL-10 and tolerogenic dendritic cells
6. C-protein coupled receptors on cells through-out body activated by SCFA, & SCFA block histone-deacetylases ==> increases acetylation of enzymes in the control of the NK-kappa-beta signalling pathway
:. SCFA inhibits NF-KB signalling pathways
7. improving diet –> increases gluterate = decreases neuroinflammation
* can be used to treat depression, Parkinson’s and autism
8. also useful in suppressing airway inflammation –> asthma = should eat more fibre
Microbial component: PSA
PSA = polysaccharide A from Bacteroides fragilis –> absorbed through gut epithelium
- in CD4+ T cells = enhancement of Treg cells –> TGFbeta produced –> TH17 & TH1 responses are dampened down ==> overall suppression of immune system
* N.B. immune system designed to have a level of suppression otherwise = over-active
* if there is no fibre = overactive immune system
probiotics
live microorganisms that when administered in adequate amounts confer a health benefit for the host
pre-biotics
non-digestible food ingredients that, when consumed in sufficient amounts selectively stimulate the growth/ activity of a limited number of microbial genera or species in the gut that confer(s) health benefits to the host
bacteriotherapy
transplantation of the entire ecosystem (Faecal transplants)
