8-1: The Human Microbiome Flashcards
How many bacterial genes are there for every human gene?
~100
What is the human microbiota? What is another name for it?
Collection of microbes living in/on us. Also called “microbial flora”
What is the human microbiome?
Microbiota and the environment they live in.
What is dysbiosis?
Term used to describe microbiota that is unhealthy for the host. “out of balance” - loss of commensals, increase in microbes associated with disease.
What does the majority of our knowledge regarding the microbiome come frome?
16s DNA shotgun sequencing and animal models
What are some things we know very little about regarding microbiota?
Community dynamics, how microbes interact
Links between microbiota and disease: causal or correlative?
Mechanisms linking microbiota and disease
Ways to restore healthy microbiome to individuals with dysbiosis
How are microbiota of people similar? How are they different?
Similar at phylum level, but also unique in each individual at species level
Microbiota composition depends largely on which two factors?
Mostly environmental factors, some genetic component.
At what age is microbiota established? What’s interesting about this?
Established at a young age, and very resilient to changes.
What problems can microbiota resilience and loss of resilience lead to?
Loss of resilience can lead to dysbiosis, while resilience makes interventions in the microbiota difficult.
Where are the microbes in/on our bodies?
Gastrointestinal tract (stomach, small intestine, colon)
Skin
Oral cavity/upper respiratory tract (mouth, nose, throat)
Urogenital tract (urethra, vagina)
Most internal sites of the body are considered what?
Sterile - no bacteria
How does microbiome vary by location?
Different parts of the skin, saliva, urogenital tract and GI tract have very different compositions of organisms
Describe the composition of the stomach microbiota.
Low pH tends to keep numbers low, but a microbial community still exists
What part of the GI tract has the densest microbial population?
Density increases as you progress through the GI tract, so the large intestine
What factors vary throughout the GI microbiome?
pH, O2 and nutrients
What protects the epithelium that lines intestines of the GI tract?
Mucous layer
What is mucous?
Thick and slippery suspension that includes antimicrobial factors and mucin
What is mucin?
Gel-like glycoprotein substance that serves as a barrier
Where do most microbes remain in the GI tract?
Lumen and NOT in direct contact with host cells
What feeds the GI tract population?
Nutrients in food, some of which we can’t digest
What percent of fecal matter is made of bacteria?
30%!
How is the gut microbiota variable?
Person-to-person differences, where the abundance of different genera varies by orders of magnitude
Even most abundant genera are missing from some people
What are the three major phyla of the gut microbiota
- Bacteroidetes: g(-)
- Firmicutes: g(+)
- Proteobacteria: facultative anaerobes. Maintain anaerobic environment by consuming any O2 present
High proportions of which phyla is indicative of dysbiosis?
Proteobacteria
What is the major form of metabolism in the gut? What is the minor form?
Major - Fermentation
Minor - aerobic respiration
What are primary fermenters?
Usually Bacteriodetes. Break down diverse carbohydrates from food or mucin.
What do primary fermenters produce?
Short chain fatty acids that are absorbed by the host, or fermentation products that feed other organisms (syntrophy)
How is the gut microbiota important for human health? (4)
- Compete with pathogens to prevent colonization
- Digest food (eg. fiber to short chain fatty acids)
- Produce nutrients we can’t make (vitamins, AA)
- Promote healthy immune system
What is the dominant symbiotic relationship we have with our gut flora?
mutualistic
What can disruptions to microbiota early in life (eg. antibiotics) cause?
Asthma, allergies, etc
What causes dental plaques?
Formation of biofilms on teeth
What is Staphylococcus aureus responsible for?
It is an opportunistic pathogen that if exposed to cuts/wound, can lead to infection.
What can S. aureus produce?
Potent virulence factors, causing life threatening infection
What dominates vaginal microbiota? What do they do?
Lactobacillus species, which lower vaginal pH (~5) via fermentation end products (lactic acid) to preent infection
What does low vaginal pH prevent? What happens when it is high?
Prevent infection with pathogens. Reduced lactobacillus increases pH allowing candida albicans to bloom, causing yeast infection
What is a probiotic?
Live microorganisns that have a bacterial effect on the host. Consuming “good bacteria”.
What is a prebiotic?
A substance, that when consumed, promotes the growth of beneficial microbes. Eg. fiber
What are fecal transplants?
Fecal matter from a healthy donor transplanted into dysbiosis patient, to reintroduce normal/healthy microbiota.
What infection can fecal transplants cure?
Clostridoides difficile infections
