26 - gut microbiota

why does bacteria change along GIT

different O2 requirements/concentrations

different pH

different transit times (different bacterial growth rate)

functions of gut microbiota

METBOLISM of dietary components

PRODUCTION of essential metabolites to maintain health

DEVELOPMENT of immune system - immune priming

HOST SIGNALLING - gut brain axis

MODIFICATION of host secretions

DEFENCE against pathogens

why is bacteria good for including fibre in diet

bacterial fermentation of fibre: -

- releases additional phytochemical

- maintains slightly acidic pH

- increases commensal bacterial population and pH improves resistance to pathogens

- essential supply of short chain fatty acids

left side - metabolism of gut microbiota

left side = most common site of intestinal disease

- very little fermentable carbohydrates

- pH neutral

- turnover slow

right side metabolism of gut microbiota

right side = site of most bacterial fermentation

- carbohydrate rich

- pH middle acidic

- rapid turnover

2 parts of colonisation resistance

barrier effect

- large number of indigenous microbiota prevent colonisation by ingested pathogen AND inhibit overgrowth of potentially pathogenic bacteria normally resident at low levels

active competitive exclusion

- conferred by both microbe-microbe and microbe-host interactions

local effects of bacterial fermentation

pH lowering

pathogen inhibition

increased calcium absorption

effects of antibiotics on gut microbiota

broad spectrum target pathogens but also kill commensal bacteria changing composition

reduced bacterial diversity

increased proteobacteria

opportunity for pathogen colonisation - C. Diff can occur due to this

overgrowth of C. Diff after antibiotics causes....

toxin production resulting in

- abdominal pain

- fever

how does FMT work and how is it good for C. Diff infection

faecal sample from healthy screened donor transplanted into C Diff patient

donor microbiota repopulates inside large intestine

displacement of C. Diff preventing infection

restores healthy gut microbiome that has been disrupted by repeated antibiotic use

what are probiotics

live microorganisms that when administered in adequate amounts confer a health benefit on host

what are prebiotics

substrate that is selectively utilised by host microorganisms conferring a health benefit

what are the 3 mechanisms of action of probiotics

1. widespread - carried out by many bacteria

2. frequent - whole groups of bacteria

3. rare - few bacteria or strains

widespread action of probiotics

competition

competitive exclusion

barrier function

reduce inflammation

frequent action of probiotics

bioconversions of dietary products

direct antagonism - fighting pathogens

immune stimulation

rare action of probiotics

production of vitamins e.g. vitamin K

systemic effects of prebiotics

metabolic

- increase insulin sensitivity decreasing lipid accumulation

- increase barrier function reducing inflammation

satiety

- increase PYY and GLP-1 secretion

- increased satiety meaning decreased food intake

immunodulatory

- increased immune system

- decreased inflammation

- decreased allergic reactions

bone

- increased calcium

infant

- in formula - pathogen exclusion and lactate formation

short chain fatty acid products and function

butyrate - intestinal epithelial cell growth and regeneration

propionate - gluconeogenesis in liver and satiety signalling

acetate - transported in blood to peripheral tissues, lipogenesis

impacts of junk food on bacterial activity

doesn’t reach large intestine, doesn’t feed gut microbes

energy absorbed in stomach/small intestine. >70% energy uptake

metabolism of high fat and protein associated with less healthy metabolites

impact of high fibre foods on bacterial activity

e.g. fruit, veg, pulses, whole grains, absorbed in large intestine, 5-10% energy uptake

feed the gut microbiota, metabolism of high fibre foods produces good protective metabolites

fermentation of high fibre foods releases short chain fatty acids → slightly acidic pH → resist against pathogen colonisation → improves population of resident microbiota

causation and correlation with respects to microbes and disease

altered gut microbiota composition is associated with many disease, does not always mean the microbiota CAUSES the disease

what does probiotics help to treat

antibiotic associated diarrhoea

traveller’s diarrhoea

irritable bowel syndrome