Ch 14 - Normal Human Microbiota

What is symbiosis?

A relationship between organisms

What is commensalism?

When one organism benefits and the other is unaffected

What is mutualism?

When both organisms benefit

What is a microbiota?

The total community of microbes associated with an organism or a defined habitat

What is a microbiome?

The composition of microbial genomes in a habitat

What is the human microbiota?

The total community of microbes associated with the human body

What is a virome?

Total community of viruses and phage

What is a transient microbiota?

Microbes that inhabit a habitat for a temporary period, often acquired from the environment

What is colonization?

The ability of a microbe to attach to a body surface and replicate

What is adhesions?

Genermal term for factors that allow microbes to attach to a surface and colonize

What is bioburden?

The number of microbes that typically inhabit an environment, microbial load

What is dysbiosis?

An imbalance in the microbiota brought on by infection, antibiotics, new foods, emotional stress, etc., can lead to disease or infection

What is the gut-brain axis?

The connection between the GI tract an the CNS, links the gut microbiome to nerologicl function, endocrine signaling, and immunity

What is the vangus nerve?

The main connector in the gut-brain axis

What are the benefits of having a microbiome?

Help digest food, synthesize compounds, microbial antagonism, training immune system via immunomodulins

What are immunomodulins?

Substances produced by the microbiota that modulate our immune system

What is microbial antagonism?

When normal the normal microbiota interferes with the colonization of a pathogen

What are the risks of having a microbiome?

Antibiotic resistance, opportunistic pathogens, dysbiosis, etc.

What is a gnotabiotic animal?

An animal that is germ-free or in which all microbial species present are known, typically have a poor immune system, thin intestinal walls, higher risk of infection, etc.

What defenses does the skin have against bacteria?

Acidic (pH of 4-6), salty (secretions from exocrine glands), dry, secretions often contain lysozyme

What kind of bacteria mainly live on the skin?

Gram-positive bacteria that are resistant to drying and halotolerant, skin has microenvironments depending on location that changes microbial composition

What defenses does the eye have against bacteria?

Tears help to rinse the eye and contain lysozyme, organisms in the eye are mostly transient

What defenses does the mouth have against bacteria?

Mechanical motion of swallowing and saliva contains lysozymes

How do the emergence of a baby’s teeth change their microbiome in their mouth?

Anaerobes colonicze and change the environment, bacteria form a glycocalyx that adheres them to the oral surface and each other (helps them resist being dislodged by saliva) and allows them to easily form biofilms

What defenses does the upper respiratory tract have against bacteria?

Microbes entering via inhalation usually get trapped in the nose by cilia and mucus, ultimately get funneled to the stomach

What is unique about tonsils?

They have crypts that allow for anaerobes to grow

What defenses does the lower respiratory tract have against bacteria?

Mucociliary escalator, alveolar macrophages help destroy microbes

What is the mucociliary escalator?

Ciliated mucous lining of the lower respiratory tract, sweeps foreign particles and microbes up and out of the lungs

What defenses does the stomach have against bacteria?

Acidic, mucous lining (contain pits that are less acidic and can support the growth of some microbes)

What happens to stomach acid if a person is malnourished?

Malnourishment can cause a loss of stomach acid and open the door for opportunistic pathogens

What kind of microbes live in the intestines?

Anaerobes and facultive anaerobes

What defenses does the duodenum and jejunum have against bacteria?

Slightly alkaline (basic), some microbes can produce bile salt hydrolase to survive

What defenses does the ileum and cecum have against bacteria?

Anoxic, slightly acidic, less bile

What defenses does the large intestine/colon have against bacteria?

Anoxic, slightly acidic

What part of the body has the highest bioburden?

Large intestine/colon

How do methanogens lead to weight loss?

H2 is produced as a result of fermentation, H2 has negative feedback on fermentation, methanogens eat H2, effectively lowering their concentration and result in less negative feedback on fermentation, this allows fermentation to increase resulting in weight loss

How can fecal transplants help with weight loss?

Lean people typically have higher ratios of bacteroidetes and firmicutes, when fecal matter from a skinny person is transplanted into a fat person, that person is able to lose more weight, if fecal matter from a fat person is transplanted into a skinny person, it has little to no effect

What defenses does the vagina have against bacteria?

Mildly acidic (pH 4.5), vaginal secretions inhibit the growth of many microbes

How are microbes restricted to their locations?

Via tight junctions

What are tight junctions?

Hold together layers of epithelial cells to create a barrier (e.g. blood-brain barrier, placental barrier, etc.), regulated to allow some immune cells to pass

What are probiotics?

Food or supplements with live beneficial bacteria

What are prebiotics?

Foods with indigestable fibers meant to promote growth of healthy microbes

What are some examples of microbiome therapy?

Pro/prebiotics, fecal microbiota transplant, phage therapy, etc.

What is the hygiene hypothesis?

Speculation that our modern world has led us to not get enough natural exposure to microbes early on in life