What is the definition of microbiota?
“Assemblage of microorganisms present in a defined environment”
*most things can be considered to have their own microbiota e.g. soil will have its own defined microbial community (all unique)
What is the definition of human microbiota?
“The total microbial community that resides both on and within us”
*total microbial community ON and IN the host. Every human has their own microbiota (oral cavity, gut, skin etc)
What does the number of bacterial cells depend on?
Number depends on how recently you have been to the toilet (majority of bacterial cells reside in the colon)
Are there more bacterial cells or human cells?
Bacterial cells outnumber human cells but not by that much
1.3 : 1
What is the Sterile womb hypothesis?
- suggests we are sterile prior to birth (womb is sterile unless there is a complication)
- Acquisition occurs during birth - vaginal delivery is exposed to lactobacilli
- C section bypasses vaginal delivery – exposed to surgical and human skin microorganisms
- This gives slightly different microbiotas depending on route of birth
What is the alternative theory to the sterile womb hypothesis?
- In utero colonisation
- theory that the womb is not sterile and that it is colonised with gram negative bacteria
- Based on identification of ‘DNA’ from placenta and amniotic fluid
*although evidence is lacking
When does the development of the microbiota reach a peak?
Develops over time and reaches a climax community at around 3yrs old
What does the development of the microbiota depend on?
- Environment e.g. how much sun skin is exposed to
- Diet (breast milk or formula, weaning? Breast milk and formula nutrients are very similar but cannot mimic all the several hundred different types of bacteria I breast milk that colonises within the child drinking it)
- Antibiotic exposure in infancy?
Is microbiota the same for any 2 people?
NO - everyone has a slightly different one
Where does most bacteria reside in the human body?
The large bowel
What are 5 parts of the large bowel?
- Caecum
- Ascending
- Transverse
- Descending
- Rectum
What does the microbiota act as?
microbiota acts as a metabolic organ. Activities contribute to health and can also cause disease
What are the 2 most important bacteria when talking about gut communities?
Firmicutes and Bacteroidetes (phylums)
How will Eastern vs western populations have different gut communities?
Different diets
What is Firmicutes and what does it mean?
- Firmicutes – means ‘strong cell wall’ and it is a phylum
What is Staphylococcus and what does it mean?
- Genus
- Staphylococcus’ meaning grape like coccus (in ancient Greek)
What is aureus and what does it mean?
- Species
- aureus
What are the 3 roles of the gut microbiota in health?
- Induction of intestinal angiogenesis
- Colonisation resistance
- Metabolism of carbohydrates and proteins
What happens during the induction of intestinal angiogenesis?
- development of villus capillary network
- very complicated
- bacterium induces angiogenesis
- Bacteroides thetaiotaomicron
What occurs during colonisation resistance?
- Microbiota in the body takes up all free available space to colonise – this limits the space for pathogens that want to adhere to space and produce toxins
- Second route: microbiota is using up all the free nutrients for a supply of energy – less going round for potential pathogens
- Microbiota may change the pH by producing organic acids and make the environment unfavourable to pathogens
- A barrier to potential pathogens
- Production of antimicrobials
What happens during the metabolism of carbohydrates and proteins?
- Fermentation of non-digestible carbohydrates (cellulose, resistant starch, inulin) –> microbiota breaks these down in the later stages of the gut
- Fermentation product from breaking down these non-digestible carbs are gas and short chain fatty acids (e.g.) butyrate, propionate, acetate
- Diet provides nutrients for host and the residing microbiota
What can the short chain fatty acids produced during fermentation be used as?
Can be used as an energy source for the cells lining the colon, but also known to have anti-carcinogenic and anti-inflammatory properties
What was the difference between obese and lean phenotypes in mice?
- Lean phenotype was more balanced to fermicutes
- When put on the same diet, and the Obese phenotype lost weight, microbiota started to become more similar
- Mice eat their own poo, so if they’re in a mixed cage, the obese phenotype will be consuming the lean phenotypes poo colonising itself with bacteroidities – started to alter the metabolic profile to lean
- By increasing bacteroidites, you see a reduction in food consumption (due to altered microbiota)
*Feeding fat mouse skinny poo makes it skinny
Feeding skinny mouse fat poo makes it fat
What leads to a reduction in weight in humans?
- increase dietary fibre
- introducing short chain fatty acids
- Inulin is broken down by bacteria present in the lower part of gut
