chapter 24 - microbial symbioses with humans Flashcards
What is a microbiome?
a functional collection of different microbes in a particular environmental system
What is a microbiota?
describes all microbe in a microhabitat
What are the heavily colonized body regions for microbes?
- gastrointestinal tract
- oral cavity and airways
- urogenital tracts
- skin
What is the role of the microbes in the gut and what do they affect?
- digestion of food
- absorption and production of nutrients
they affect early development, health and predisposition to disease
How does the colon hold microbiota?
an in vivo fermentation vessel, they use nutrients derived from the digestion of food to survive.
How does the large intestine hold microbiota?
restricted to the lumen of the large intestine, others go in the mucosal layer
What is the bacterial diversity in the large intestine and colon
composed of a few phyla
mostly bacteroidetes and firmicutes
What are the 3 different types of enterotypes that everyone has?
- enriched in bacteroides
- is in prevotella
- is enriched in ruminococcus
What are different outcomes from microbial metabolites and transformations?
- vitamin production
- modification of steroids
- amino acid biosynthesis
Where are the microbiota located in oral cavity?
- saliva contains antimicrobial enzymes
- high concentrations of nutrients near surfaces in the mouth promote localized microbial growth
Where are microbiota located in the airway?
- bacteria enters upper respiratory tract from the air during breathing
- most are trapped in the mucus and then expelled by swallowing or sneezing
- lower respiratory tract has no normal microbiota in healthy adults
What moves cells up and out of the lungs?
ciliated mucosal cells
Where are the microbiota located in the urogenital tracts?
- kidney and bladder are sterile
- epithelial cells of urethra are colonized by facultative aerobes
- altered conditions causes infections (like uti)
What are the three different kinds of microenvironment when it comes to skin?
- dry skin
- moist skin
- sebaceous skin
How many microbiota are found on the skin?
10 to the 10 skin microorganisms covering the average adult.
How do we become colonized with microbes?
throughout life, bacterial diversity increases whilst interindividual variability decreases
Why is vaginal delivery the first major step in microbial colonization?
because there is a massive exposure to maternal vaginal and fecal microbiota
What are the changes seen in the gut microbiota during pregnancy?
1- vaginal microbiota diversity decreases,
- Lactobacilli dominance increases with age
that ensures pH remains low, which limits bacterial diversity.
This prevents bacteria from ascending to the uterus
2- gut microbiota diversity also decreases
- high energy yielding fecal microbiota dominance increases with age
causing greater energy harvest during pregnancy to support the growth of mother and fetus
What is the difference between vaginal delivery and cesarean delivery?
- Vaginal: introduced to vaginal microbes
normal introduction of gut microbes
normal immune system development
production of specific cytokines - Cesarean delivery: introduced to skin flora
abnormal microbial introduction
disrupted intestinal microbial colonization
risk of asthma, allergies, celiac etc
Why is breastmilk good for babies?
contains: lactose, fats and HMO
HMO cannot be digested by the baby, they are actually metabolized by bacteria in large intestine.
What does HMO promote?
1- gut epithelia cell-to-cell adhesion
2- produces sialic acid, necessary for brain development
3- protects against pathogens (resembles gut glycans)
What is the relationship between stability and richness of adult microbiome vs age
the older you get the more richness you get
the older you get the more stability you get, until retirement where you become less stable
Why can mice be used to do experiments?
- they have a short life cycle
- they have well-defined genetic lines
- can experiment on them rather than humans
What type of research has been done on mice?
- importance of host genetic background through selective gene knockout
- effect of microbiota community composition using germ free mice colonized with different bacteria
- influence of tightly controlled diets
- consequences of antibiotic treatment
- physiological traits through fecal transplants
How does gut microbiota play a role in obesity?
obese people have more Firmicutes than non-obese people. The low H2 promotes fermentation leading to weight gain.
What is the role of microbiota in IBS
there is a low diversity of microbiota in people with IBS
there are changes in temporal stability and metabolic activity of microbiota
There is an increase in firmicutes and a decrease in bacteroidetes
Explain the microbiota-gut-brain axis
Plenty of chemicals produced that are active in the brain as neurostimulation chemicals.
They can get into the brain and change things in the neurodevelopment.
What does maternal immune activation (mIA) involve?
involves elevated levels of inflammatory factors in the blood, placenta and amniotic fluid during pregnancy that can be caused by viral or bacterial infection
is a profound risk factor for neurochemical and behavioural abnormalities in offsprings
What is the role of anitbiotics?
oral antibiotics decrease ALL microbes in the human gut
What is the role of probiotics?
live organisms that confer health benefits to host
What are prebiotics?
typically carbohydrates that are indigestible by human host, but provide nutrition for fermentative gut bacteria
