Microbiota of the GI Tract Flashcards
what does transit time effect?
bacterial populations present and exposure to toxins
what changes in bacterial populations along the GI tract?
> conditions are increasingly anaerobic
increase in bacterial density
increase in dominance of obligate anaerobes
define facultative anaerobic bacteria
they can grow in the presence of oxygen and the absence of oxygen
define obligate anaerobes
they cannot grow in the presence of oxygen (are rapidly killed)
why does the dominant bacterial species change along the GI tract?
> different o2 concentrations
different ph
different transit time
what does GI bacteria do?
> metabolises > produces essential metabolites > develops the immune system > defends against pathogens > modifies host secretion
what sort of food do gut microbes grow on?
fibre (fruit, vegetables, pulses and whole grains.
other than food what do gut microbes use for growth?
endogenous (host-derived) substrates
what is the effect of fibre in our diet on transit time?
it shortens it
what does fibre contain that is good for us?
> phytochemicals
anti-oxidants
vitamins
what is the result of bacterial fermentation of fibre?
> release of phytochemicals
maintains acidic ph: improving resistance to pathogens
increased commensal bacterial population
essential supply of short chain fatty acids
what is the function of butyrate?
> epithelial cell growth and regeneration
what is the function of propionate?
> gluconeogenesis in the liver
> satiety signalling
what is the function of acetate?
lipogenesis
how does metabolism of gut microbiota differ from the left side of the colon to the right?
> right side is carbohydrate rich while the left has little carb. fermentation
right has low ph compared to left which Is neutral
turnover is rapid on the right but slow on the left
what is the effect of a diverse and balanced diet on microbiota and their products?
it creates diverse and balanced microbiota and diverse and balanced products
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
name the two ways colonisation creates pathogen defence
> barrier effect
> active competitive exclusion
what can happen if the mucus layer is disrupted?
the bacterial cells can penetrate the mucous layer and epithelial barrier causing inflammation
at what ph’s do pathogens normally grow optimally?
> ph6 or above
what part of the colon has the most pathogen exclusion?
the proximal colon due to its low ph
why might there be more disease in the distal colon?
there is a higher ph so less pathogen exclusion as well as a slower transit time
what can dysbiosis of gut microbiota composition lead to?
disruption of homeostasis and gut inflammation
what is the greatest influence to microbiota through life?
dietary changes
describe the changes of microbial diversity through life
baby: low diversity
adult: high diversity
frail elderly: low diversity
define dybiosis
a general imbalance in microbiota composition that an be implicated by many disorders
what is the likely cause of inflammation in IBD?
dysregulated host immune response to the gut microbiota
what evidence is there that microbes play a role in IBD development?
> increased bacterial load
host genes have been identified that are involved in bacterial recognition and are important for IBD development
spectrum of antibiotics can reduce the symptoms
feacal stream diversion induces remission in chrons disease
it does not occur in germ free animals
in IBD is increased or decreased bacterial diversity observed?
decreased
what is the effect of antibiotic use in terms of IBD?
it reduces bacterial diversity and increases enterbacteriaceae
how does inflammation alter microbial composition?
it decreases the mucus barrier therefore increasing oxygen exposure altering the microbial composition, this then leads to inflammation
how may diarrhoea alter the microbial composition of the gut?
it decreases the transit time causing a alteration in gut microbial compistion
what prebiotic can be given to patients to relieve symptoms of IBS?
specific ones designed to boost numbers of faecalibacterium prausnitzii
define probiotic
live microorganisms which when administered in adequate amounts confer a health benefit on the host
define prebiotic
this is a substrate that is selectively utilised by host microorganisms conferring a health benefit, food for resident bacteria
do probiotics become permanent residents in a healthy gut?
no
name some wide spread mechanisms of action for probiotics
> competition
competitive exclusion
barrier function
reduce inflammation
name some frequent mechanisms of action for probiotics
> bioconversion
direct antagonism
immune stimulation
name a rare, strain specific action of a probiotic
> production of vitamins
name some health benefits attributed with prebiotics
> improved gut function > reduce colon cancer risk > increase calcium absorption > can lower glycaemic MORE EVIDENCE IS NEEDED HOWEVER TO PROVE THESE EFFECTS COMPLETELY, HENCE EFSA STOP THE USE OF WORDS "PROBIOTIC" AND "PREBIOTIC"
what can short and long term antibiotic therapy lead to in terms of gut microbiota?
> loss of diversity
recovery of altered diverse population (resistance genes)
pathogen colonisation
what can overgrowth of c. diff result in?
> toxin production
abdominal pain
fever
what are c. diff spores resistant to?
antibiotics
what is the initial treatment for clostridium difficile associated diarrhoea?
antibiotic therapy (works 75% of the time)
in recurring c.diff associated diarrhoea what is the best treatment?
FMT: faecal microbial transplantation
describe faecal microbial transplantation
> faecal sample form screened volunteer donor is transplaned into recipient
enema, colonoscopy, naso-gastric enteric tube, capsules
donor microbiota displaces c.diff preventing reinfeciton
what is the criteria for microbials taken from a donor stool sample for FMT?
> sensitive to antimicrobials
easy to culture
representative of gut commensual bacteria
increased consumption of what may reduce the risk of colon cancer (WHO)
dietary fibre
