Microbiota of the GI tract Flashcards
What is the transit time in the mouth?
Up to 1 minute
What is the transit time in the oesophagus?
4-8 seconds
What is the transit time in the stomach?
2-4 hours
What is the transit time in the small intestine?
3-5 hours
What is the transit time in the colon?
10 hours to several days
What does transit time affect?
Bacterial populations
Cell exposure to toxins
What increases moving don the GI tract?
Anaerobic conditions
Bacterial density
Dominance of obligate anaerobes
What is the most bacterial dense site of the GI tract?
Large intestine
What is the predominant colonisation of the large intestine?
Anarobes
What are facultative anaerobes?
Can grow in presence or absence or oxygen
What are obligate anaerobes?
Cannot grow in the presence of oxygen
What factors affect the dominant bacteria at each site?
pH
Transit time
O2 concentration
What is the pH of the mouth?
Neutral
What is the pH of the stomach?
Acidic
1.5-4
What is the pH of the duodenum?
Neutral
7-8.5
What is the pH of the ileum?
Acidic
4-7
What is the pH of the colon?
5.5-6.5
What is the role of the GI microbiota?
Metabolism of dietary components Production of essential metabolites Development of immune system Host signalling Defence against pathogens Modifications of host secretions
How does the GI microbiota metabolise dietary components?
Microbes grow on fibre and convert it to other products
What are the benefits of including fibre in the diet?
Improves faecal bulking
Contains important phytochemical, antioxidants and vitamins
What is the purpose of bacterial fermentation of fibre?
Release additional phytochemicals
Maintains slightly acidic pH
Increases commensal bacterial population and resistance to pathogens
Essential supply of short chain fatty acids
What short chain fatty acids does fibre supply and what is their purpose?
Butyrate- epithelial cell growth and regeneration
Propionate- gluconeogenesis and satiety signalling
Acetate- lipogenesis
How do resident bacteria protect against pathogens?
Lower pH
Create physical barrier
Prime immune system
Produce active components to ‘kill’ incoming pathogens
What is the barrier effect?
Large number of indigenous microbiota prevent colonisation by ingested pathogens and inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels
What is the gut mucosal immune system?
Mucous layer of the gut forms barrier between lumen bacteria and epithelial cells
When do autoimmune disease of the gut occur?
When immune system can no longer distinguish between harmful pathogens and commensal bacteria
How does the breakdown of fibre help with signalling?
Short chain fatty acids produced act on receptors on epithelial cells to secrete hormones and have the desired effect
What factors influence gut microbiota>
Dietary changes- greatest influence
Age
Alcohol intake
What is changes in microbiota composition associated with?
Disease
This does not mean this is necessarily the cause
How might diseases be cause by indigenous microbiota?
Overgrowth
Colonisation at a different body site
General dysbiosis
What is inflammation in IBD likely caused by?
Dysregulated immune response to microbiota
What microbiota changes are present in IBD?
Reduced bacterial diversity
Reduced stability in bacterial composition
Increased mucosal barrier load
What is the treatment of IBD?
Broad spectrum antibiotics
Faecal stream diversion
Why is it difficult to distinguish between the cause and effect of IBD?
Reduced bacterial diversity could be caused by inflammation or antibiotics
What are probiotics?
Live microorganisms which, when administered in adequate amounts, confer a health benefit
What are the different mechanisms of action of probiotics?
Competition Bioconversion Production of vitamins Direct antagonism Competitive exclusion Barrier function Reduce inflammation Immune stimulation
What are probiotics?
Selectively fermented food/ingredient that results in specific changes in composition and/or activity of GI microbiota, conferring health benefit on the host
What is the effect of antibiotics on microbiota?
Kill pathogen but also commensal bacteria
What are the consequences of antibiotic therapy?
Decreased microbial diversity
Opportunity for pathogen colonisation and pathogen dominant community
What happens with C. diff post antibiotic therapy?
C. diff expands to occupy empty niches
Overgrowth causes toxin production, fever, abdomen pain, C. diff associated diarrhoea
What is the initial treatment of C. diff infection?
Antibiotic therapy
What is the treatment for recurring C. diff infections?
Faecal microbial transplant
