Microbiota of the gut

Question 1

Understand why there are differences in bacterial communities through the GIT

Answer 1

Factors which affect microbiota:

• Transit time
• Ph
• Anaerobic/aerobic conditions

Transit time:

• Mouth: 1 minute
• Oesophagus:4-8 seconds
• Stomach:2-4 h
• SI:3-5 hours
• Colon:10 h

Anaerobic conditions:

• Increase down tract
• Number of obligate anaerobes increases
• In stomach: facultative anaerobes
• In the colon : obligate anaerobes

Facultatitive anaerobic bacteria: bacteria that can live in both aerobic and anaerobic conditions
Obligate aerobic bacteria: bacteria that have to live in aerobic conditions

Down the GI:

• Transit time increases
• Anaerobic conditions increase
• Number of gut bacteria increase

Question 2

Understand the activities of different bacterial species

Answer 2

• Digestion of metabolites
• Immunological function
• Modification of host secretions
• Host signalling

Question 3

Explain why the presence of/products of bacteria are important for a healthy gut
(Digestion of metabolites)

Answer 3

Carbohydrates broken down into butyrate, acetate, proportionate
Butyrate: used for epithelium and cell proliferation
Proportionate: used for gluconeogenesis in the liver
and satiety signalling
Acetate: used for lipogenesis in peripheral tissues

Question 4

Explain why the presence of/products of bacteria are important for a healthy gut
(Host signalling)

Answer 4

SFCA acts as receptors to epithelium in GI and trigger hormonal production

• FFAR2- inhibits fat accumulation
• FFAR3- improves insulin resistance and co-ordinates satiety impulses to the brain
• GPR-109A- suppresses colonic inflammation

Question 5

Explain the impacts of different diets on bacterial activity

Answer 5

• Improves faecal bulking, shorter transit time, eases passage
• contains important anti-oxidants, phytochemical
• Improves bacterial fermentation: increases the number of phytochemical and essential short chain FA, improves the number of commensal bacteria, maintains a slightly acidic ph

Question 6

Explain the effect of antibiotics on the gut microbiota

Answer 6

Wide spectrum antibiotics (most commonly used) are effective against both pathogenic bacteria as well as commensal bacteria

• Reduces diversity of commensal bacteria
• Can lead to proliferation of resistant bacteria
• Resistant bacteria transfer genes between each other through conjugation, transformation, transduction
• Increased diversity of bacteria- which has now been transformed

Question 7

Understand the difference between probiotics and prebiotics

Answer 7

Probiotics: live microorganisms which confere a health benefit
Prebiotics: foods consumed which can be used as a substrate by microorganisms in the body to produce a positive effect

Question 8

Understand the potential of probiotics in ‘treating’ disease, and which disease

Answer 8

How do they work?

• competition
• Reduce inflammation
• Immune stimulation
• Bioconversions
• Barrier function
• Direct antagonism

They do not become an integral part of the GI system but their actions and products can have beneficial effects.
They have be proven to improve GI disease- however as they are so diverse their action cannot be qualified.

Question 9

Understand when prebiotics might be useful

Answer 9

• Improved gut transit time and stool bulking
• Reduces risk of colon cancer by reducing cell proliferation
• Adding to baby formula can increase bifidobacteria numbers
• Can be used to increase bone density