EXAM Lecture 12

Question 1

Where does the microbiota come from

Answer 1

the colonization of microbiota accelerates at birth but doesnt start there

used to believe that the uterus was sterile and microbiota colonization started after birth BUT studies have detected bacteria in the placenta, umbilical cord, amniotic fluid, and meconium (evidence bacteria from mom can cross placenta)

after parturition, microbial colonization is from:
- mother (vaginal (not in c section birth), fecal, skin
- environment
- diet (especially intestinal microbiota)

breast fed babies gut microbiota is mainly dominated by bifidobacterium compared to babies nourished with formula (lactobacillus)

Question 2

Mode of delivery impacts babies gut microbiota composition

Answer 2

• vaginal delivery has more diversity vs C section which is lower diversity
• pre term babies have less diversity vs full term (less time to develop, usually fed thru IV instead of breast or bottle)
• the window for proper gut microbiota development is narrow

Question 3

Gut microbiota and liver

Answer 3

your gut microbiota collectively do as much metabolic work as your liver

liver is a vital organ and so is the gut microbiota:
- redundancy in disease is bad but good in microbiome because it provides a back up when bacteria are killed (antibiotics, etc)
- high gene count is good for microbiome because this means high functional capacity (with some redundant functions)
- low gene count = low functional capacity

our microbes are vitally important, but we work to exterminate them (hand sanitizer, disinfectant, etc)

Question 4

Microbial diversity differs vastly in different tissue organs

Answer 4

• skin microbiota exhibits regional diversity differences (ex butt vs back are very different)
• within colon microbiota, proximal colon differs from distal

regional differences in:
- composition
- diversity
- abundance
- gene counts

Question 5

extinction events may impact health

Answer 5

hygiene hypothesis:
- we are preventing proper colonization by being too clean

missing microbiota hypothesis
- we are disturbing proper colonization across generations through antiobiotic use, etc
- antibiotics use especially in early childhood can be problematic
- critical window in development that is susceptible to changes in the microbiota
- antibiotics decrease abundance and diversity in microbiota which impacts disease susceptibility later in life

many studies have shown:
- gut microbiota changes with antibiotic use
- takes long time afterwards to return to baseline (composition (diversity and abundance))
- sometimes does not return to baseline at all (permanent shift in microbiota) “one bacteria dies out, allows other bacteria to increase abundance which disrupts balance”
- repeated hits cause vast changes from which the ecosystem cannot recover

Question 6

Balance: important for host and microbiota

Answer 6

eubiosis:
- balance

symbiont:
- bacteria with known health promoting functions

commensal:
- permanent residents of the microbiota
- provide no benefit or detriment
- part of the phylogenetic core

pathobionts:
- permanent residents of the microbiota that have the potential to induce pathologies or adverse host effects
- “low abundance”
- keep these bacteria in check by other commensal bacteria; if these commensal bacteria die, pathobionts have the chance to grow and take up a larger % abundance of microbiota composition, damaging the host

dysbiosis:
- typically negative loss of balance associated with host disease or loss of physiological function
- unnatural shift in composition of microbiota (reduction in # of symbionts/commensals and/or increase in # of pathobionts)

result:
- non specific inflammation which may predispose susceptible people to inflammatory diseases caused by pathogens OR increase ability of pathogens to colonize that tissue and alter the microbiota composition

Question 7

Factors effecting microbial dysbiosis

Answer 7

best case: microbiota in babies born by vaginal delivery, roomed-in with mother, and breast fed

worst case: C section, admitted into ICU, formula-fed, administered IV and antibiotics

other factors:
- host genetics
- lifestyle (diet, stress)
- early colonization (birth in hospitals, formula fed, etc)
- medical practices (antibiotcs, hygiene); antibiotics do not distinguish between symbionts, commensals, pathobionts

there is no concencus on what is a healthy or optimal microbiota composition

Question 8

factors that can impact gut microbiota

Answer 8

Host dependent factors:
- genetic background
- age (declines with age)
- sex and sex hormones
- immune system
- gut motility

Treatment:
- antibiotics
- gastric bypass (decreases absorption)

Diet (substrate for microbial fermentation):
- non digestible carbs - fermented by microbiota
- protein - fermentable
- fat
- prebiotics or probiotics

prebiotic: functional non digestible food component that stimulate the activity or growth of bacteria and promote host physiological function

probiotic: usually live microorganisms which when administered in adequate amount confer a health benefit on the host (yoghurt, etc)