microbial interactions Flashcards
by how much do microbial genes outnumber human genes
100:1
why is the small intestine a harsh environment for microbial life
1) short transit time
2) excretion of digestive enzymes and bile
why does the colon have a higher diversity and density than the small intentestin
no digestive secretion
nutrient more environment
longer transit time
what does the colon and bacteria exchange in the relationship
bacteria get a nice environment and the colon has the ability to digest complex carbohydrates and boots immune system fending off pathogens
what affect can oral antibiotics have on the gut
kill the gut micorbiome reducing diversity and exposes the host to opportunistic pathogens such as e.coli
outline how the gut microbiome is assembled in a stepwise manner
1) colonization starts at utero
2) the bacteria aquired from mothers is soon displaced by infants own bacteria
3) increases in richness of bacteria as infants move from milk based diet to adult
what order to bacteria colonise the gut
1) firmicutes
2) proteobacteria
3) actinobacteria
4) bacteroidetes establish after solid food is introduced
why bacteria are most dominant in the host as it ages
firmicutes and bacteriodetes
what correlation was found between individuals with obesity and bacterial gut diversity
individuals with obesity are less diverse than a healthy individual
what is dysbiosis
an imbalance between types of organisms present in a persons natural microflora
what do bacteria get from us
- microbes dont need to make aminoacids as they are supplied by the intestinal epithelium
- live in a protected environment
what do we get from bacteria
- break down and ferment complex carbohydrates and generat short chain fatty acids
what happens to the short chain fatty acids produced by firmicutes and bacteriodetes
f= absorbed by the colonic epithelium and used as a dominant energy source
B= distributed by the blood stream to peripheral organs for energy production and a precursor for cholesterol and amino acids
what does fermentation produce and what is it broken down into
formate
broken down into co2 and hydrogen
what do methanogenic bacteria do with the co2 and hydrogen produced by formate
remove hydrogen produced by fermentaion as it inhibits fermentation
uses co2 as a last electron acceptor and produced methane as a byproduct
how are opportunistic bacteria kept at bay in the gut
short chain fatty acids help drop the PH of the intestine and control growth of harmful bacteria
what is syntrophy
the interaction where one species feeds off of metabolic products of another
what do bacteria do in the gut of rumens
help to digest cellulose by degrading and fermenting plant derived polymers to provide nutrients to the host
what is commensalism
a relationship where one partner benefits while the other is left unaffected such as bacteria in the mouth
outline the commensal relationship between the host and mouth bacteria
bacteria colanise teeth and build multispecies biofilms which feed off food debris that stick to it
however if left it can grow pathogenic bacteria leading to cavity formation and gum disease
what is parasitism
bacteria which cause infectious disease where the bacteria gains and the host looses
what challenges does an infectious agent have to confront
1) encounter- host and bacteria must meet first
2) entry - cant occur without penetration of tissue e.g. ingestion or inhalation
3) establishment- must overcome host defences
what is vibrio cholerae
a moltile gram negative bacteria which inhabits lakes and rivers
most strains rarley cause disease
outline how v,cholerae can become pathogenic
pathogenic strains contain pathogenicity islands, bacteriophages infect prey (bacteria) and transfer this pathogenicity island via transformation or transduction
what is a pathogenicity island
regions that encode amongst other genes and cause it to become pathogenic
e.g.
CT and TCP
what does the cholera toxin cause and how
an influx of water into the lumen of the intestine which causes watery diarrhea from the activation of adenylate cyclase which fills cells with cAMP and chlorine causing water to follow the gradient into the lumen
what is listerias monocytogene bacteria
gram positive, faculative anaerobe which lives in the soil and can cause food poisoning
what characteristic does l.monocitogenes have
can tolerate refrigeration, freezing, high salt and low moisture and can evade phagocytosis by the hosts defence
how does l.monocytogenes escape phagocytosis
1) pokes holes in the phagosome by secreting pore-forming toxins (listeriolysin)
2) uses actin tails to propel itself within the cell cytoplasm into adjacent cells
what is mutualism
where both partners gain
