6 - The Gut Microbiome Flashcards
What is the gut microbiome
The ecosystem of microorganisms (mainly bacteria) living in the gastrointestinal tract, especially the stomach, small intestine, and large intestine
How dense is the microbial population in the gut
The large intestine can contain up to 100 trillion microbial cells per millilitre
Why does the gut microbiome thrive in the intestines
Due to a large surface area, a nutrient-rich environment, oxygen gradients creating niches, structured microbial communities, and constant replenishment via diet
What types of microorganisms make up the gut microbiome
Bacteria (dominant), archaea, viruses, and fungi
What are the dominant bacterial phyla in the gut
Firmicutes
Bacteroidetes
Actinobacteria
Proteobacteria
When does microbial colonisation begin
At birth — vaginal delivery introduces birth canal microbes, while C-section introduces skin microbes
What maternal factors influence early microbiome development
Maternal microbiota, antibiotic use, and feeding method (breastfeeding vs formula)
How else is the infant microbiome shaped
Through environmental exposure (family, pets) and dietary transitions (e.g. introduction of solid food)
How does the microbiome evolve over time
New microbes compete with existing ones; the microbiome changes significantly in the first two years, stabilising in adulthood
What is the adult ‘core microbiome’
A relatively stable community mainly composed of Firmicutes and Bacteroidetes
How does the microbiome aid digestion
It breaks down otherwise indigestible food components, extracting nutrients and energy
How does the gut microbiome support metabolism
It influences drug metabolism, bile acid recycling, and fibre digestion
How does gut biome protect against pathogens
Through production of inhibitory compounds, physical barriers, and immune signalling
What role does gut biome play in immune development
It helps train the immune system, particularly through microbes like Bacteroides and Bifidobacterium
How does gut biome modify compounds
It alters bile acids and other host-related molecules
What vitamins are synthesised by the gut microbiot
B vitamins and vitamin K
How does the gut microbiome influence systemic health
Through microbial metabolites that affect mood, sleep, and overall body function
How does it maintain gut homeostasis
By supporting physiological balance and maintaining a stable ratio of Firmicutes to Bacteroidetes
What is eubiosis
A balanced and diverse gut microbiome state that supports health
How can we maintain a healthy microbiome
Through a fibre-rich diet, prebiotics, probiotics, limiting unnecessary antibiotics, and supporting ecological balance
What are prebiotics
Special carbohydrates that nourish beneficial microbes
What are probiotics
Live microbial supplements that support gut health
What is the ‘core microbiome’ in adults
A stable microbial community mainly consisting of Firmicutes and Bacteroidetes
What is dysbiosis
An imbalance in the microbial community of the gut
What are signs of dysbiosis
Altered microbial composition, phylum-level shifts, overgrowth of pathogens (e.g. E. coli), and loss of beneficial bacteria
What can cause dysbiosis
Antibiotics, diet, ageing, disease states (e.g. IBD, T2D), and external environmental factors
What are the systemic effects of dysbiosis
It can affect mood (gut-brain axis), skin health (gut-skin axis), and respiratory function (gut-lung axis)
What is IBD and how is it linked to the microbiome
A chronic inflammatory GI condition associated with gut dysbiosis and reduced microbial diversity
What are the two main forms of IBD
Crohn’s disease (CD) and ulcerative colitis (UC)
What is the global impact of ulcerative colitis
It affects over 5 million people, especially in Western countries, with rising cases worldwide
What microbial changes occur in IBD
Increased facultative anaerobes, decreased microbial diversity, and lower production of SCFAs (short-chain fatty acids)
What is the difference between UC and CD
UC causes superficial inflammation limited to the mucosa; CD involves full-thickness (transmural) inflammation of the intestinal wall
