Topic 19: Human Microbiome Flashcards
Describe briefly human exposure to foreign and resident microbes and the microbes’ reactions when entering human’s body
Human body is constantly exposed to foreign and resident microbes, including exterior surfaces and cavities.
The microbes may fail to colonize or become either short or long-term resident.
Compare the proportion of microbes by weight, by number, by genes and their implications
Even though bacteria only takes up very small proportion (2%) of the body’s weight, they make up 70% of the total number of cells and more than 99% by genes.
Mirobial metagenome is much larger than human genome which means they have much higher metabolic potential, helping with digestion and metobolism.
Where should and should not microbes be found in our body?
Microbes are present most densely in the gut, but they are excluded from the underlying tissues.
Identify and describe 3 traditional classification of microbes/bacteria
- Parasitism: partner 1 benefits, partner 2 harmed –> host better without parasites
- Commensalism: partner 1 benefits, partner 2 neutral –> host unchanged without/with commensal
- Mutualism: partner 1 and 2 benefits –> host needs mirobes for optimal fitness
Identify some complications that may happen without the presence of microbes
- Gut functions - decreased digestive capacity
- Immune functions - no adaptive immunity
- Metabolic regulation - altered neuro-endocrine signaling pathways
- Cognitive fucntions and mood - underdeveloped enteric NS
Explain how bacterial numbers differ between the stomach, small intestine, and colon
The number of microbes in the colon is much higher compared to stomach and small intestine.
The reason is digestion happening in stomach and small intestine relies on the secretion of acids, enzymes, and bile. However, non-starch polysaccharides and the cell walls in plant-based food, which is fibre, is digestion-resistant which means it cannot be digested by those exocrine secretions.
Microbes in the colon have a much wider repertoire of carbohydrate-degrading enzyme than humans, so their presence in the colon can help solubilize the non-starch polysaccharides.
Identify and describe the metabolic pathway prefered by microbes (process and products)
Bacteria in the gut release enzymes to break down non-starch polysaccharides and resistant starch into individual sugars which can be up-taken by the microbes.
Microbes then perform fermentative metabolism to produce short chain fatty acids which is a valuable energy sources for colon cells, the microbes/bacteria growth and other tissues.
Describe the differences in the GI tract of herbivores
Herbivores consume a diet composed mainly of fibres which required a large number of microbes to digest efficiently.
–> Herbivores evolved to have either large hindgut or large foregut (a specilized fermentation chamber) in order to house larger “fermentative microbial communities
Identify and describe mechanisms of microbiome management
- Nutrient control: population size and activity
+ Directs bacteria to use fibre by rapidly abosrbing other nutrients
+ Selects for fermentative metabolism by excluding oxygen and iron (central for respiratory)
+ Supports growth on fibre by adding back nitrogen fertilizers (supporting bacteria)
+ Limits total bacteria biomass by exreting feces often and removing excess microbes
==> Encourage functions we need - Immune functions: location or contain bacterial activity in gut
+ Intestinal mucosal surface limits bacterial contact with epithelium
+ Immune defenses kill bacteria at epithelium
+ The adjoining intestinal tissue (lamina propria) is kept sterile (no microbes present)
==> Punish activites we don’t need
Which two ways may result in negative impacts on health?
Either delivery of harm or loss of benefits
Identidy and differentiate features of pathogens/parasites and cooperators
- Pathogens/parasites:
+ Normally not present
+ Presence may lead to diseases
+ Experimental infection is sufficient to cause diseases
==> “Specialist Pathogens” - excluded from the body - Cooperators/Commensals/Mutualists:
+ Normally present
+ Absence may lead to abnormal physiology
+ If absent may lead to loss or decrease of existing benefits whic indirectly result in diseases
==> “Potential Pathogens” or “ Opportunistic Pathogens” - encourage in some parts and exclude in others
Describe how pathogens can directly and indirectly cause damage to the host
Pathogens will first colonize on the external surface or internal cavities/mucosal surface inside the body
- Direct:
+ Obstruction
+ Production of toxins/tissue-destructive enzymes
==> damaged/impaired functions
- Indirect:
+ The colonization triggers DAMPs - pro-inflammatory signals from cell damage or the damage on the host may also send MAMPs - pro-inflammatory signals from microbes - which induces immune responses
+ Immune responses may include: inflammatory leading to apoptosis, or may produce specific antibody - The immune responses can be resolved by the removal of pathogens and normal functions can be restored
- Still, failure to resolve the responses or altered immune tone can lead to pathological negative outcomes
Explain why the up-regulation and down-regulation of immune responses need to be balanced
- Down-regulation of immune responses to avoid collateral damage to our cells (damage to innocent cells)
+ If immune responses are too weak, more susceptible to infections and cancers - Up-regulation of immune responses to exclude microbes from our body
+ If unable to regulate, allergies, autoimmunity and inflammatory disorders may occur - Immune responses also need to be site-appropriate (different in lumen and underlying tissues)
What is dybiosis?
Dybiosis is refering to diseases caused by a poorly functioning symbiosis/microbiome
When does our body develop the regulation of microbial beneficial functions and the immune regulation to prevent microbial invasion?
This happens through post-natal development.
The baseline of microbial and immune homeostasis emerged during post-natal development can be deviated by other factors like antibiotics, diet, lifestyle, etc., resulting in diseases.
