Lecture 7

Question 1

what experiment was done with the dog and the bell?

Answer 1

scientist rang bell every time before giving dog food, when the bell rang, juices were secreted in the intestine, so that the food would be ready to be digested.

Question 2

what’s the difference between healthy and germ-free mice’s mucus and epithelial cells?

Answer 2

in germ free mice, the mucus layer is minimal and the gap between gap junctions isn’t as tight.

Question 3

how does Bacteroides thataiotaomicron protect us from the pathogen Citrobacter rodentium?

Answer 3

via consumption of common limited nutrients and starving the invading pathogen. Bt takes up carbohydrates used by the pathogen Citrobacter rodentium, leading to a competitive nutritional exclusion of pathogen from intestine.

Question 4

how do SCFAs inhibit salmonella virulence?

Answer 4

they down regulate virulence genes in the salmonella.

Question 5

which pathogen can SCFAs inhibit growth of?

Answer 5

Enterohaemorrhagic E. coli

Question 6

what are bacteriocins?

Answer 6

antimicrobial proteins produced by bacteria that can kill or block growth of competing bacteria.

Question 7

what can Bacteroides thuringiensis secrete, and what does it target?

Answer 7

it can secrete a bacteriocin, thuricin CD, which targets spore forming Bacilli and Clostridias including C. difficile.

Question 8

what bacteriocin can E. coli produce?

Answer 8

bacteriocins such as colicin- which directly inhibits growth of related strains, e.g. EHEC.

Question 9

what does enterococcus faecium express?

Answer 9

anti-listeria bacteriocins.

Question 10

what did in silico analysis of human gut microbiota genomes reveal?

Answer 10

600 candidate biosynthetic gene clusters encode small molecules.

Question 11

what does the microbiota do to bile acid?

Answer 11

it converts it to secondary bile acids which are anti-bacterial.

Question 12

do germ-free mice have many secondary bile acids?

Answer 12

no, they have a very little amount.

Question 13

do antibiotic treated mice have many secondary bile acids?

Answer 13

antibiotic treated mice contain recedes levels of secondary products.

Question 14

what does specific depletion of microbiota converting bile acids to secondary factors enable?

Answer 14

colonisation by C. difficile

Question 15

what is indole?

Answer 15

a microbial metabolite of tryptophan. it attenuates bacterial virulence.

Question 16

what happens to salmonella that’s exposed to indole?

Answer 16

it becomes less invasive for epithelial cells and macrophages in vitro.

Question 17

what effect does indole have on ehec?

Answer 17

it reduces EHEC attachment to intestinal epithelial cells and biofilm formation.

Question 18

what can indole and SCFAs do together to salmonella?

Answer 18

they synergistically repress salmonella pathogenicity island 1 (SPI-1) genes which are important for invasion.

Question 19

what does monocolonisation of germ-free mice with Bacteroides fragilis do?

Answer 19

it promotes development of CD4 t lymphocytes.

Question 20

what do segmented filamentous bacteria drive?

Answer 20

differentiation of CD4 lymphocytes into th17 cells.

Question 21

what negative effect can our microbiota have?

Answer 21

microbiota can produce metabolites which can enhance bacterial virulence.
eg. Bt can cleave silica acid residues from mucin, and generate succinate, leading to enhanced colonisation of C. difficile.

Question 22

what effect does the microbiota using host mucin to generate fucose or succinate have?

Answer 22

it can enhance the virulence of EHEC via the locus for enterocyte effacement.

Question 23

what do C. difficile spores need to germinate?

Answer 23

microbiota produced secondary bile acids.

Question 24

what can microbiota derived di-hydrogen be used for?

Answer 24

used by salmonella to jump-start growth.

Question 25

what does microbiota produced ethanolamine do?

Answer 25

its a nitrogen source and regulator of virulence genes in EHEC and salmonella.

Question 26

antibiotics are bactericidal and bacteriostatic, what does this mean?

Answer 26

they indiscriminately target both bad pathogenic and good beneficial bacteria
therefore it can rapidly reduce microbiota composition and diversity.

Question 27

what are the effects of antibiotic treatment?

Answer 27

it reduces colonisation resistance, susceptible to C. diff and salmonella.

Question 28

what does C. dififcile colonise?

Answer 28

the large intestine.

Question 29

what are the two C. diff toxins, what do they do?

Answer 29

TcdA and TcdB enter and damage epithelial cells, leading to inflammation.

Question 30

what do C. diff and salmonella catabolise?

Answer 30

silica acid as a carbon source to promote growth bloom.

Question 31

what does antibiotic treatment enhance?

Answer 31

enhances release of host-derived silica acid.
triggers production of the microbiota-derived nutrient succinate
succinate and silica acid promote expansion of C. diff