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MEDS1001 > human microbiome > Flashcards

human microbiome Flashcards

(47 cards)

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1
Q

The microbes we are exposed to may…

A
  • fail to colonize (then die)
  • become short-term residents (live for short time, body prevent it from being long-term)
  • become long-term residents (shape our life history)
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2
Q

Do we have microbes in utero?

A

No! However after birth the residence of TRILLIONS of microbes is normal

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3
Q

Microbial metagenome is much larger than
human genome?

A

True

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4
Q

The presence of microbes in tissues is…

A

NOT normal.

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5
Q

Tight gut barrier

A

mucin layer over tightly joined epithelial cells
* excludes microbes from the underlying tissues of our body
* mucin layer - lubricating barrier

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6
Q

Parasitism

A

Partner 1 benefits - increased growth output for parasite/pathogen
Partner 2 harmed - reduced growth output for ‘host’
Host better without parasite

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7
Q

Commensalism

A

Partner 1 benefits - increased growth output for commensal
Partner 2 neutral - no growth change for host
Host same with/without commensal

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8
Q

Mutualism

A

Partner 1 benefits - increased growth output for mutualist
Partner 2 benefits - improved growth for host
Host needs microbe for optimal fitness

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9
Q

In the absence of Microbes…

A
  • Gut functions are different – reduced digestive capacity
  • Immune functions are different – essentially no adaptive immunity
  • Metabolic regulation is different – altered neuro-endocrine signalling pathways
  • Cognitive functions & mood are different – underdeveloped ENS
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10
Q

The gut microbiome develops…

A

at approximately the same time postnatal development finishes.

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11
Q

factors in normal microbiome development

A
  • microbe exposure (birth canal, skin)
  • infant diet (breast milk)
  • immune sytem development
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12
Q

disturbances to microbiome development

A

cause deviations from microbial homeostasis
* antibiotics (at birth or during infancy)
* microbe exposure (C-section, infection)
* diet (breast/formula; weaning pattern)

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13
Q

deviance from immune homeostasis

A

cause immune-mediated diseases in later childhood
* asthma
* atopic disease
* T1D
* Crohn’s & Colitis

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14
Q

gut microbiome

A

the stable resident microbial community of a defined habitat (gut) in an individual person.

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15
Q

Bacterial numbers in stomach & small/large intestine

A
  • Stomach - continually exposed to microbes, but very few actually grow there.
  • Distal Small intestine (mainly ileum) - site of stable occupation by microbes. Lower numbers than colon.
  • Large intestine (colon) - has distinct conditions for microbial growth and far higher microbe cell density than ileum.
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16
Q

Over 98% of the total microbial cells in our gut are Bacteria .

A

true!

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17
Q

Bacteroidetes (10-90% of all cells)

A
  • Tens to hundred of Bacteroidetes species
  • Vast majority show fermentative metabolism
  • Diverse growth substrates commonly polysaccharides
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18
Q

Firmicutes (10-90% of all cells)

A
  • Hundreds of Firmicutes species.
  • Vast majority show fermentative metabolism.
  • Diverse growth substrates commonly polysaccharides
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19
Q

Proteobacteria (1–5% of all cells)

Study These Flashcards
A
  • Tens of Proteobacteria species.
  • Respiratory and fermentative metabolism
  • Growth substrates rarely polysaccharides, commonly small molecules (sugars, amino acids and fatty acids).
20
Q

Methanobrevibacter (1-2%)

Study These Flashcards
A
  • One or two species.
  • One type of metabolism (methanogenesis).
  • Growth on one-carbon compounds and hydrogen.
21
Q

The presence of microbes changes our food requirements

Study These Flashcards
A
  • Quantity - Less food is eaten by animals that are colonised.
  • Quality - The diet fed to germ-free animals requires vitamin supplementation and a simple carbohydrate profile.
22
Q

Small intestine

Study These Flashcards
A

Tank for further hydrolysis.
* Cells of accessory organs secrete enzymes and bile.
* Intestinal epithelial cells absorb nutrients.

23
Q

Stomach

Study These Flashcards
A
  • An acid hydrolysis tank.
  • Gastric cells secrete acid and enzymes
24
Q

Material passing to the colon includes…

Study These Flashcards
A

Indigestible - chemically inaccessible to human enzymes (e.g. fibre)
Inaccessible – particle structure prevents enzyme access (e.g. intact corn kernel)
Excess – exceeded digestion/absorption capacity of small intestine.

25
Plant cell walls...
are digestion resistant (e.g. cellulose, xylan). * Starch must be released to be degraded by amylases. * Other storage polysaccharides of plants are typically also digestion-resistant (e.g. inulin, arabinogalactans).
26
Ruminants Vs. Humans
Ruminants: up to 70% of calories via rumen microbes Humans: 10 – 15% of calories via colon microbes
27
Plant specialists
have **complex** digestive tract with a specialised **fermentation** chamber
28
meat-specialists
**simple** digestive tract
29
Short Chain Fatty Acids
SCFA are **fermentation metabolites** that are valuable energy sources for animals
30
Most common metabolism is Fermentation Simple Carbs to...
* Acetate, CO2, H2 * Propionate, CO2, H2 * Butyrate, CO2, H2 * mixed SCFA, CO2, H2 * human energy sources : intestinal gases
31
Sulphate reduction
A specialised respiratory metabolism * SCFA -> CO2 + H2S * Toxic molecules
32
Other bioactive microbial metabolites include...
* Bile acid derivatives DCA and LCA * Neurotransmitter production (serotonin, GABA) * Vitamin production * Amino acid production * human essential nutrients
33
The net effect of microbial metabolites on our health is a product of:
* Food items/diet * Microbial activity * Types of microbes * Adaptive responses
34
“Nutrient control”
determines population size and activity in the gut (encourages functions we need): * Body **directs bacteria to use fibre** - rapidly absorbs other nutrients * Body **selects for fermentative metabolism** – excludes oxygen, removes iron * Body **supports growth on fibre** - adds back nitrogen ‘fertiliser (uric acid, urea) * Body **limits total bacterial biomass** - poops often * Bacteria **trained to ‘do the right thing’**: stay in gut, grow on fibre, release SCFA
35
Immune functions contain bacterial activity within the gut (Punish activities we don’t need)
* Intestinal mucosal surface limits bacterial contact with epithelium * Immune defences kill bacteria at epithelium. * The lamina propria (adjoining intestinal tissue) is kept ‘sterile’ * Bacteria near the wrong place, or in the wrong place, are not tolerated
36
Microbe interaction with immune system
* Immune system has functions in **preventing** and **resolving** **infections** at all body sites. * Immune system is also potentially dangerous – today chronic diseases involving **immune-metabolic dysfunction** are the major health burden
37
Key features of Pathogens
* **Not** normally present * Presence is associated with **disease** consistently * Experimental infection is sufficient to cause disease. * “Specialist pathogens” * EXCLUDE from body
38
Key features of Commensals
* Normally **present** * Absence leads to **abnormal physiology** (in experimental Germ-free animals). * May indirectly contribute to disease * "Potential pathogens” * “Opportunistic pathogens” * ENCOURAGE in some parts and EXCLUDE from others
39
Defence against pathogens involves...
1. **Colonisation** *resistance* 2. **Barrier** functions 3. **Immune** functions
40
Pathogens can colonise...
* on **external** body surface (skin, teeth etc.) * internal **cavity** (gut lumen) * internal **mucosal** surface (epithelium of lung etc.)
41
direct effect of pathogen
produce toxin or tissue-destructive enzyme OR Obstruction
42
MAMPs
Microbe-associated Molecular Patterns
43
DAMPs
Damage-associated Molecular Patterns
44
Immune tone
* **Differences** in immune tone are major factors in different infectious disease **severity**. * **Change** in immune tone is a major factor in development of **chronic** diseases. * The **gut microbiome** is a factor in modulation of immune tone.
45
Dysbiosis
a term for diseases of a poorly functioning symbiosis
46
Is our risk for infection tightly inter-related with our microbiome?
YES - Opportunistic pathogens typically co-occur with normal microbes in our gut and specialist pathogens can invade our gut.
47
The biggest disease burdens today are characterised as...
**chronic immuno-metabolic** diseases. * Nearly all of them are nutrition-related and microbiome-related

MEDS1001 (21 decks)

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