Chapter 24: Microbiome

Question 1

microbiome

Answer 1

assemblage of microorganisms on and in the diverse regions/habits of the body

Question 2

gastrointestinal microbiota

Answer 2

human gi tract
comprises 400m^2 of surface area
digestion of food, absorption of nutrients, production of nutrients aided by microbial flora
contains 10^13 to 10^14 microbial cells
microbiota influenced by diet and physical conditions

Question 3

stomach microbiota

Answer 3

10^4 cells/g
firmicutes, bacteroidetes, actinobacteria in acidic lumen
proteobacteria in gastric mucosa
helicobacter pylori present in 50% of people, risk of chronic inflammation, cause peptic ulcers

Question 4

small intestine microbiota

Answer 4

10^8 cells/g
anaeronic fusobacterium

Question 5

large intestine microbiota

Answer 5

10^12 cells/g
fermentation vessel
facultative aerobes (e. coli) in low numbers
obligate aerobes (clostridium, bacteroides)
yeast candida albicans (eukaryote)
bacteria in lumen and outer mucus layer
bacteria make vitamin K, B12, 9/20 AAs

Question 6

gut overview

Answer 6

90% all human gut phylotypes fall into 1 of 3 major bacterial phyla: firmicutes, bacteroidetes, proteobacteria
individuals can be dominated by any one
no correlation with ethnicity or diet, shared by family members
influencs health, obesity, drug therapy

Question 7

immune system

Answer 7

immune system does not properly develop in absence of microbial stimulation
early life exposure to variety of microorganisms essential to develop tolerance for beneficial microorganisms and recognize harmful ones
excessive hygiene in young kids promotes autoimmune conditions

Question 8

germ free mouse study

Answer 8

immaturity of gut associated lymphoid tissue, decreased serum immunoglobulin levels, underdeveloped thymus and spleen

Question 9

gnotobiotic mice

Answer 9

mice in which every microorganism present is defined
germ-free mice one class

Question 10

gut colonization

Answer 10

not entirely understood
difference in naturally born vs c-section infants
breat-feeding vs formula influences microbiota and immune system development
gut of natural birth breast fed infants primarily bifidobacteria
microbiota develops until 3 years old

Question 11

functions of gut microbiota

Answer 11

protective: pathogen displacement, nutrient competition, receptor competition, production of antimicrobial factors
structural: barrier fortification, inductionof IgA, apical tightening of tight junctions, immune system developments
metabolic: control IEC differentiation and proliferation, metabolize dietary carcinogens, synthesize vitamins, fermentation, ion absorption, salvage energy

Question 12

other functions of gut

Answer 12

sensory
neuroendocrine
nervous
immune
serotonin production

Question 13

bacterial balance

Answer 13

enhancing beneficial bacteria of gut can treat intestinal disorders
influences: age, diet, susceptibility to infection, use of antibiotics or other drugs, excess alcohol, immunologic status of host, exposure to toxic substances, ph, transit time

Question 14

concept of probiotics

Answer 14

elie mechnikoff proposed bacteria in fermented milk can control bacterial fermentation in intestinal tract

Question 15

probiotics

Answer 15

usually dairy food, dietary supplement containing live bacteria
replace or add to beneficial bacteria in gi tract

Question 16

examples of probiotics

Answer 16

lactobacillus, bifidobacteria, enterococcus, lactococcus, streptococcus, saccharomyces/yeast

Question 17

mechanism of action of probiotics

Answer 17

competitive effects from occupation of normal colonization sites, direct antagonism through natural antimicrobial compounds (bacteriocins), competition for nutrients, enhancement of immune system, increase absorption of vitamins and minerals

Question 18

prebiotics

Answer 18

non-digestive food ingredient that beneficially affects host by selectively stimulating growth and/or activity of limited number of bacteria
can also block pathogens

Question 19

actions of prebiotics

Answer 19

non-digestibility, selective fermentation by potentially beneficial bacteria in colon, alteration of composition of colonic microbiota towards a healthier composition

Question 20

SCFA

Answer 20

short chain fatty acids
aka VFAs
main source of energy for colonic epithelial cells

Question 21

gut microbiota and clinical disease

Answer 21

inflammatory bowl disease and obesity

Question 22

Inflammatory bowel disease (IBD)

Answer 22

chronic inflammation of git
diarrhea, blood in stool, weight loss, abdominal pain
not caused by specific microorganism
imbalance between immune system and normal gut flora
microbiome shows less functional capacity
possibly causes: early antibiotic treatment, protein rich diet

Question 23

obesity

Answer 23

excessive body fat
increases risk of other diseases: heart disease, diabetes, high blood pressure, cancer
not caused by specific pathogen
in mice: energetic imbalance of gut flora, more firmicutes and methanogenic archaea, stronger H2 consumption –> more turnover in fermentations, increases acetate, propionate, butyrate taken up

Question 24

a. muciniphila

Answer 24

study of highly beneficial microbe
mice with a. muciniphila had 50% less body weight under high fat diet
less fat mass
no insulin resistance or inflammation
safe for humans
lower levels in of serum and cholesterol