The gut microbiota in Health and Disease

Question 1

Factors that affect the gut microbiota (7)

Answer 1

probiotics
prebiotics
antibiotics
Faecal transplant
Environment 
Diet 
lifestage

Question 2

What happens to the gut bacterium in sepsis

Answer 2

it translocates into the bloodstream

Question 3

IBD and gut microbiota

Answer 3

Inflammation in IBD likely results from a
dysregulated host immune response to the
gut microbiota

IBD doesn’t occur in germ-free animals

Question 4

Individuals with IBD have reduced…

Answer 4

bacterial diversity

Question 5

What are Firmicutes

Answer 5

Firmicutes are a phylum of bacteria, most of which have gram-positive cell wall structure.

Question 6

What features of IBD could affect the microbiota? (5)

Answer 6

Antibiotic use

Inflammation - decrease in mucus barrier - increased O2 exposure - altered microbial composition

Diarrhoea (affects transit time)

Host diet - may be a desire to eat less fibre - changes composition of microbiota

Host genotype

Question 7

What can be caused by broad-spectrum antibiotic use?

Answer 7

Reduced bacterial diversity and increases in Enterobacteriaceae (gram -ve, includes E-Coli etc)

Question 8

What are probiotics?

Answer 8

live microorganisms which, when administered in adequate amounts
confer a health benefit on the host

added live bacteria - actimel, activia etc

Question 9

what is a prebiotic?

Answer 9

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

food for resident bacteria - in some plants or added to cereal etc

Question 10

How do probiotics work? (8)

Answer 10

1. . Competition
2. Bioconversions (diet)
3. Production of vitamins
4. Direct antagonism (pathogens)
5. Competitive exclusion
6. Barrier function
7. Reduce inflammation
8. Immune stimulation

Question 11

Name some types of prebiotics

Answer 11

FOS + inulin

GOS

Lactulose

Resistant starch

Beta glucan

Question 12

Natural sources of prebiotics (3)

Answer 12

Garlic
Leeks
Onion

Question 13

What health benefits are associated with prebiotics? (5)

Answer 13

Improved gut function
- stool bulking and faster gut transit

Prebiotics may reduce the risk of colon cancer
- reduced DNA damage and cell proliferation, faster gut transit

Prebiotic (GOS/FOS) supplementation of infant formula increases
bifidobacteria numbers

Prebiotics (FOS/Inulin) increase calcium absorption and bone health
pH effect

Consumption of prebiotics instead of sugars can lower glycaemic index
induce a lower blood glucose rise after meals compared to those containing sugar

Question 14

What are common antibiotic targets (4)

Answer 14

cell wall synthesis
Vancomycin
β-lactams

DNA/RNA synthesis
Fluoroquinolones
rifampicin

Folate synthesis
Trimethoprim
Sulfonamides

Protein synthesis
Macrolides
Aminoglycosides

Question 15

What are common antibiotic resistance mechanisms

Answer 15

Efflux - pump antibiotic out of the cell and prevent accumulation

Immunity and bypass
or
Target modification
prevents antibiotic affecting normal target

Inactivating enzymes
- destroy antibiotic activity

Question 16

What are the consequences of long or short-term antibiotic therapy

Answer 16

Most antibiotics are broad-spectrum antibiotics
active against target pathogen but also ‘kill’ commensal bacteria - loss of diversity

Antibiotic treatment also causes the spread of antibiotic resistance - through conjugation, transformation or transduction

Question 17

What are the consequences during and immediately post- antibiotic treatment

Answer 17

Decreased microbial diversity

Opportunity for pathogen colonisation

Results in pathogen dominated
community

Clostridium difficile expands to occupy
empty niches following antibiotic therapy

Overgrowth of C. difficile results in toxin production, abdominal pain, fever (CDAD)

C. difficile spores are resistant to antibiotics
+ some strains are antibiotic resistant

Results in recurring C. difficile infections

Question 18

Clostridium difficile associated diarrhoea: initial treatment and treatment for recurring infections

Answer 18

antibiotic therapy - cures approx 75% of patients

For recurring infections (when antibiotics don’t work) best treatment found to be FMT

Question 19

What is Faecal microbial transplantation

Answer 19

stool transplantation

Effective in >90% of patients with recurring C. difficile infections

Question 20

How does Faecal microbial transplantation work

Answer 20

Faecal sample from screened healthy volunteer donor transplanted into recipient (enema, colonoscopym naso-enteric tube)

donor microbiota repopulates large intestine, displaces c.dificile, prevents reinfection

very successful for recurring Clostridium difficile associated diarrhoea - CDAD - but not other GI diseases