Theme 2: Microbiota Flashcards
What are enterotypes, and how are they defined?
Enterotypes are classifications of gut microbiota into distinct clusters based on microbial co-occurrence patterns.
They are mainly grouped into three types:
- Enterotype 1 – Dominated by Bacteroides (associated with protein and fat-rich diets)
- Enterotype 2 – Dominated by Prevotella (associated with high-fibre, carbohydrate-rich diets)
- Enterotype 3 – Dominated by Ruminococcus
Why do enterotypes complicate identifying microbes related to gastrointestinal disorders?
Enterotypes have been shown to not be associated with fixed human
features, such as blood type or genetic markers. Also enterotypes can
change over time, making the relation with gastrointestinal disorders
complicated.
What are the primary microbial ecosystem strategies in the small intestine and large intestine?
- Small intestine: A fast-moving, nutrient-rich environment where microbes must rapidly utilise simple sugars and amino acids. It has low bacterial diversity due to bile acids and digestive enzymes.
- Large intestine (colon): A fermentation vessel, where microbes break down complex carbohydrates, producing short-chain fatty acids (SCFAs). It has high bacterial diversity and a stable community.
Why does the microbial diversity increase from the small intestine to the large intestine?
The short transit time and bile acids in the small intestine limit microbial colonisation. In contrast, the colon has a longer transit time and more complex substrates, allowing for a more diverse and stable microbial population.
How does an increase in Bifidobacterium correlate with increased butyrate production, despite Bifidobacterium being unable to produce butyrate?
Cross-feeding. Bifidobacterium produces lactate which can subsequently be used by butyrate producers. An increase in Bifidobacterium results and increased lactate production. Butyrate producers can benefit from this increased lactate production and hence, more butyrate is produced.
Why is butyrate important for gut health?
- It serves as the primary energy source for colonocytes.
- It reduces inflammation by inhibiting NF-κB pathways.
- It reinforces gut barrier integrity, reducing gut permeability.
What are lipoteichoic acids (LTAs), and what is their function?
Lipoteichoid acids (LTAs) are glycopolymers that are found in Gram-positive bacteria. It has been shown that LTAs induce host-specific immune responses after bacterial lysis and release into the host system. Gram-negative bacteria do not have LTAs instead they their cell wall contains LPS.
How do LTAs help distinguish Gram-positive from Gram-negative bacteria?
LTAs are only found in Gram-positive bacteria. In contrast, Gram-negative bacteria have lipopolysaccharides (LPS), which elicit strong immune responses.
What is the role of microbial fermentation in human digestion?
Microbial fermentation breaks down undigested carbohydrates (e.g., fibre, resistant starch) into short-chain fatty acids (SCFAs) such as:
- Acetate – Used by peripheral tissues.
- Propionate – Transported to the liver for gluconeogenesis.
- Butyrate – Used by colonocytes for energy.
How much of our daily energy intake is derived from microbial fermentation?
Approximately 10% of our daily energy comes from SCFAs produced by microbial fermentation.
What factors influence gut microbiota composition?
- Diet (high fibre vs. high fat/protein).
- Host genetics (some people naturally harbour different microbes).
- Antibiotic use (alters microbiota composition).
- Birth method (C-section babies have different microbiota than vaginally born babies).
- Geographical location (different diets lead to different microbiota).
How does long-term diet shape gut microbiota composition?
Long-term diets influence microbial composition:
- Western diets (high fat, low fibre) → More Bacteroides.
- Plant-based diets (high fibre) → More Prevotella.
What is Akkermansia muciniphila, and why is it important?
It is a mucin-degrading bacterium associated with:
- Improved insulin sensitivity.
- Strengthened gut barrier function.
- Anti-inflammatory effects.
How does gut microbiota shape the immune system?
Gut microbes interact with gut-associated lymphoid tissue (GALT), promoting:
- T-cell differentiation.
- Tolerance to beneficial bacteria.
- Protection against pathogens.
What is the primary application of FMT?
FMT is primarily used to treat Clostridioides difficile infections by restoring microbial balance.
How does FMT work?
A healthy donor’s gut microbiota is transferred via enema or nasogastric tube to a recipient, helping to repopulate beneficial microbes.
What are the dominant bacterial phyla in the gut microbiota?
- Firmicutes – Includes Clostridium, Lactobacillus, Faecalibacterium.
- Bacteroidetes – Includes Bacteroides, Prevotella.
- Actinobacteria – Includes Bifidobacterium.
- Proteobacteria – Includes Escherichia coli, Helicobacter.
- Verrucomicrobia – Includes Akkermansia muciniphila.
How does gut microbiota composition differ in obese individuals?
- Obese individuals tend to have a lower Bacteroidetes-to-Firmicutes ratio.
- Certain microbes promote energy harvest from food, contributing to weight gain.
How does Akkermansia muciniphila relate to obesity?
Higher levels of A. muciniphila are linked to leanness, while lower levels are associated with obesity and metabolic disorders.
What is cross-feeding in gut microbiota?
Cross-feeding is when one microbial species’ waste products serve as nutrients for another species.
Example:
- Bifidobacteria produce lactate, which is converted into butyrate by butyrate-producing bacteria.
