microbial interactions

Question 1

by how much do microbial genes outnumber human genes

Answer 1

100:1

Question 2

why is the small intestine a harsh environment for microbial life

Answer 2

1) short transit time
2) excretion of digestive enzymes and bile

Question 3

why does the colon have a higher diversity and density than the small intentestin

Answer 3

no digestive secretion
nutrient more environment
longer transit time

Question 4

what does the colon and bacteria exchange in the relationship

Answer 4

bacteria get a nice environment and the colon has the ability to digest complex carbohydrates and boots immune system fending off pathogens

Question 5

what affect can oral antibiotics have on the gut

Answer 5

kill the gut micorbiome reducing diversity and exposes the host to opportunistic pathogens such as e.coli

Question 6

outline how the gut microbiome is assembled in a stepwise manner

Answer 6

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

Question 7

what order to bacteria colonise the gut

Answer 7

1) firmicutes
2) proteobacteria
3) actinobacteria
4) bacteroidetes establish after solid food is introduced

Question 8

why bacteria are most dominant in the host as it ages

Answer 8

firmicutes and bacteriodetes

Question 9

what correlation was found between individuals with obesity and bacterial gut diversity

Answer 9

individuals with obesity are less diverse than a healthy individual

Question 10

what is dysbiosis

Answer 10

an imbalance between types of organisms present in a persons natural microflora

Question 11

what do bacteria get from us

Answer 11

• microbes dont need to make aminoacids as they are supplied by the intestinal epithelium
• live in a protected environment

Question 12

what do we get from bacteria

Answer 12

• break down and ferment complex carbohydrates and generat short chain fatty acids

Question 13

what happens to the short chain fatty acids produced by firmicutes and bacteriodetes

Answer 13

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

Question 14

what does fermentation produce and what is it broken down into

Answer 14

formate
broken down into co2 and hydrogen

Question 15

what do methanogenic bacteria do with the co2 and hydrogen produced by formate

Answer 15

remove hydrogen produced by fermentaion as it inhibits fermentation
uses co2 as a last electron acceptor and produced methane as a byproduct

Question 16

how are opportunistic bacteria kept at bay in the gut

Answer 16

short chain fatty acids help drop the PH of the intestine and control growth of harmful bacteria

Question 17

what is syntrophy

Answer 17

the interaction where one species feeds off of metabolic products of another

Question 18

what do bacteria do in the gut of rumens

Answer 18

help to digest cellulose by degrading and fermenting plant derived polymers to provide nutrients to the host

Question 19

what is commensalism

Answer 19

a relationship where one partner benefits while the other is left unaffected such as bacteria in the mouth

Question 20

outline the commensal relationship between the host and mouth bacteria

Answer 20

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

Question 21

what is parasitism

Answer 21

bacteria which cause infectious disease where the bacteria gains and the host looses

Question 22

what challenges does an infectious agent have to confront

Answer 22

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

Question 23

what is vibrio cholerae

Answer 23

a moltile gram negative bacteria which inhabits lakes and rivers
most strains rarley cause disease

Question 24

outline how v,cholerae can become pathogenic

Answer 24

pathogenic strains contain pathogenicity islands, bacteriophages infect prey (bacteria) and transfer this pathogenicity island via transformation or transduction

Question 25

what is a pathogenicity island

Answer 25

regions that encode amongst other genes and cause it to become pathogenic
e.g.
CT and TCP

Question 26

what does the cholera toxin cause and how

Answer 26

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

Question 27

what is listerias monocytogene bacteria

Answer 27

gram positive, faculative anaerobe which lives in the soil and can cause food poisoning

Question 28

what characteristic does l.monocitogenes have

Answer 28

can tolerate refrigeration, freezing, high salt and low moisture and can evade phagocytosis by the hosts defence

Question 29

how does l.monocytogenes escape phagocytosis

Answer 29

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

Question 30

what is mutualism

Answer 30

where both partners gain