Topic 8- L1 - Human Microbiome Flashcards
Human microbiota:
collection of microbes living in/on us
Human microbiome:
Microbiota and the environment(s) they live in
Dysbiosis:
a term used to describe an altered microbiota that is unhealthy for the host. Typically thought of as being “out of balance” – loss of important commensals, increase in microbes associated with disease
Most members of human microbiota are not culturable in the lab – vast majority of our knowledge comes from
DNA sequencing
16S, shotgun
similarities in microbiota of different people
(similarities at phylum level), but the microbiome composition in each
individual is unique (very different at species level)
Microbiota composition more about
environmental factors than genetic
factors…but some genetic component
Microbiota (esp. in gut) established at young age & is remarkably
resilient. Microbiota changes with different conditions…but generally
returns to original composition
Gastrointestinal tract:
Stomach, small intestine, large intestine (colon)
Stomach microbiota :
Low pH keeps numbers low,
but a microbial community exists here
Large intestines contain
Dense population of anaerobic microbes
Throughout GI tract
pH, oxygen content (generally low) and nutrients availability varies – as does the composition of microbiota
Epithelium that lines intestines protected by
mucus layer
Mucus is a thick and slippery suspension that includes
antimicrobial factors & mucin (gel-like glycoprotein substance, serves a barrier function)
Most microbes remain in
lumen, don’t directly contact host cells (there are important interactions…but there is a barrier to prevent routine, direct
physical interactions with epithelium)
Remarkable person-to-person variation
in the
gut microbiota
Bacteroidetes are
Gram-negative bacteria
– masters of complex carbohydrate
metabolism
Firmicutes is a very diverse
phylum of
Gram-positive bacteria
Proteobacteria are generally
facultative anaerobes – rapidly consume any oxygen present. Important for maintaining anaerobic environment. High proportions of can be a sign of dysbiosis.
In the guy, O2 and other common terminal electron acceptors
absent or present at low levels –
tiny bit of aerobic respiration (proteobacteria), some anaerobic respiration, but a lot of fermentation
Primary fermenters (many species, but especially Bacteriodetes)
can break down (ferment) diverse carbohydrates from food (or mucin)
- some of their products absorb short chain fatty acids
Many fermentation products feed a
range of other organisms (syntrophy)
The gut microbiota is very important for human health:
- Compete with potential pathogens – prevent/inhibit colonization
- Digest food for us. E.g. ferment fiber to short-chain fatty acids that we then absorb
- Produce nutrients (amino acids, vitamins) we can’t make – get absorbed in the colon
- Promotes a healthy immune system, “trains” immune system &
promotes immune tolerance
An example of a relatively well
established causal relationship is
Helicobacter pylori in stomach appears
to be cause of stomach ulcers
Disruptions to microbiota early in life
(e.g. antibiotics) that
reduce microbiota diversity linked to asthma and allergies
Much of the growth in oral cavities is as
biofilms (highly complex communities), especially on teeth (dental plaque)
On the skin, Some common members of microbiota are opportunistic pathogens, notably
Staphylococcus aureus, enters through cuts. Can be life threatening
Lactobacilli benefit host by
lowering vaginal pH (~5) via fermentation end products (lactic acid) – helps prevent infection by pathogens
In the vaginal microbiota, yeast (e.g. genus Candida) are part of a
healthy microbiome, but found at low levels.
Disruption of microbiome (reduced Lactobacilli, increase pH) allows these yeast to bloom, leading to a
“yeast infection”
Probiotic:
Live microorganism(s) that, when administered, have a beneficial affect on host. Consuming “good bacteria”
Prebiotic:
A substance that when consumed promotes the growth of beneficial microbes. Can be simple and effective (e.g. fiber in diet to promote healthy microbiota)
Fecal transplants:
Fecal matter from health donor transplanted into a patient - attempt to reintroduce a normal/healthy microbiota into a patient experiencing dysbiosis causing significant health issue
Fecal transplants cure to
Clostridoides difficile infections, which are highly resistant to antibiotics
