Microbiota of the Gut Flashcards
What conditions alter microbial populations throughout the GI tract?
Transit Time
Oxygen presence
pH
How does transit time affect the gut microbiota?
Slow growing bacteria wont grow in a gut section with a rapid transit time
How does O2 affect gut microbiota?
The population of the gut changes from faculative anaerobes –> Obligate Anaerobes as the gut gets more anaerobic
How does pH affect the gut microbiota?
Different sections of the gut are at different pH’s
Therefore bacteria which thrive on different pH’s grow in different areas of the gut
What are the functions of the GI microbiota?
- Metabolise dietary components/produces essential metabolites
- modify host secretions e.g. mucins and bilirubin
- Defends against pathogens
- Immune system priming
- Host signalling
How does the gut microbiota protect against pathogens?
Direct Competition - Produces active compounds that kill incoming pathogens
Priming the immune system - Training the immune system to fight bacterial infections- they help recognosise self from non-self
Barrier Function - Literally provides a physical barrier to pathogens colonising the gut
pH Inhibition - Most pathogens grow at pH’s over 6. Bacteria break down cellulose to SCFAs (mainly in the colon) which lowers the pH and inhibits pathogen growth
Why is the presence of bacteria important for the gut?
- They prevent pathogenic bacteria colonising you
- Dysbiosis of the gut microbiota can disrupt the homeostasis of the gut and lead to inflammation
- Metabolites of the microbiota are important for energy, signalling molecules and maintaining the immune system
How do antibiotics affect the microbiota?
Most are fairly broad spectrum so kill a lot of commensal bacteria resulting in a loss of diversity which leads to issues:
- Processing your diet
- Pathogenic Infection
- Maintaining the immune system
- Signalling molecules
How do antibiotics cause pathogenic infection of the gut?
antibiotics wipe out a lot of commensals
- > Opportunistic pathogenic infection, (often antibiotic resistant)
- > Toxins, abdominal pain, diarrhoea, fever etc (often CDAD)
- > Has to be treated with antibiotics
- > Viscous circle of recurrent infections
CDAD?
Clostridium Difficile Associated Diarrhoea
How do we treat dysbiosis of the gut microbiota?
A Faecal Microbial Transplant which essentially inserts the right commensal bacteria back in to begin rebuilding the gut microbia.
Do we have more microbial cells or human cells?
Microbial cells on/in our body well outnumber our own cells
What part of the GI tract is the most populated?
The large intestine, predominantly by anaerobic bacteria
What lifestyle factors change your microbiota?
Diet and Age
What is dietary fibre for?
Large intestine bacteria ferments dietary fibre. The metabolites (e.g. SCFAs) are important for health and have distant effects far outside the gut by circulating through your blood
How is commensal bacteria involved in the metabolism of diet?
Bacterial fermentation= non-digested CHO and residual proteins are broken down into gas, small chain FA, Phytochemical, vitamins, other minerals
As a result :
In proximal large intestine= large concentration of SCFA and higher PH
In distal large intestine= low conc of SCFA, low Ph
What are the SCFA produced in the LI
BUTYRATE
Propionate
Acetate
Function of the SCFA produced in the LI
Butyrate: epithelial and cell proliferation
Propionate: gluconeogenesis in the liver and satiety signalling
Acetate: Transported to peripheral tissues and used for lipogenesis
Main digestion of carbs in a day
- 40g/day
- Main products: acetate, proportionate and butyrate
- Main gas products: CO2, CH4, H2
Main digestion of proteins in a day
Protein:
- 12-18g/day
- Main products: branched SCFA, phenols, amines and indoles
- Gases: NH3 and H2S
Explain to role of gut signalling in the microbiota
- Receptors on gut epithelial cells recognise SCFA and secrete gut hormones
- FFAR2- inhibits fat accumulation
- FFAR3- improves insulin resistance and co-ordinates satiety impulses to the brain
- GPR-109A- suppresses colonic inflammation
What happens when there is a lack homeostasis between the gut bacteria and the immune system
autoimmune disease
Where are bacteria found in the gut?
In the mucosal layer which separates the bacteria from the epithelium
The mucosal layer is divided into inner mucosal layer and outer mucosal layer.
The bacteria found closer to the epithelium have more of an immune function
Different species of bacteria found in the large intestine?
- 4 phylum
- 250 genera
- 1250 species
