Micrb 265 lec 11
What shapes the infant microbiome most strongly?
Early diet, especially breast milk vs formula
What are HMOs?
Human milk oligosaccharides found in human milk
Why are HMOs so important for infant gut health?
They promote the growth of Bifidobacteria, which outcompete harmful pathogens
Can humans metabolize HMOs?
No
Can most bacteria metabolize HMOs?
No
Which bacterial group is especially promoted by HMOs?
Bifidobacteria
How do HMOs indirectly protect infants from pathogens?
They feed Bifidobacteria, which then outcompete harmful microbes
Besides feeding beneficial bacteria, what else can HMOs do?
They can bind some pathogens and help prevent pathogen attachment to the epithelium
Which organism was especially emphasized as beneficial in the infant gut?
Bifidobacterium
What major metabolites are produced especially by Bifidobacteria?
Short-chain fatty acids
What are the three main short-chain fatty acids?
Butyrate, propionate, and acetate
What does SCFA stand for?
Short-chain fatty acid
What is one major role of SCFAs in the gut?
They are an energy source for intestinal cells
How do SCFAs help gut defense?
They promote secretion of antimicrobial peptides such as defensins
How do SCFAs affect eating behavior?
They help control hormones associated with energy consumption and satiety
How do SCFAs affect the immune system?
They help tune it toward an anti-inflammatory, homeostatic state
Which type of T cell is associated with the anti-inflammatory effects of SCFAs?
Regulatory T cells
What does butyrate do to cell metabolism?
It increases beta-oxidation and represses glycolysis
What does butyrate do to the intestinal barrier?
It increases tight junction proteins
Why is butyrate especially important in infants?
It helps strengthen the gut barrier by increasing tight junctions
What does propionate do in the immune system?
It upregulates T cells of the adaptive immune system and affects recognition of foreign material
What does acetate help reduce?
Inflammation associated with colitis, arthritis, and asthma
Which feeding type is associated with more Bifidobacteria?
Breastfeeding
Which feeding type is associated with more potential pathogens such as C. difficile?
Formula feeding
Which pathogens were specifically mentioned as being elevated in formula-fed infants?
Clostridioides difficile, Citrobacter, and Enterobacter
Why might formula-fed infants have more potential pathogens?
Formula lacks the HMOs that strongly promote Bifidobacteria
What shifts the infant microbiome toward an adult composition?
Termination of breastfeeding
Does starting solid food mainly drive the shift to the adult microbiome?
No, loss of breastfeeding is the key shift emphasized
What is the major idea behind adult gut enterotypes?
Adult microbiomes can be grouped into three overlapping compositions dominated by different bacteria
What are the three adult enterotypes?
Bacteroides, Prevotella, and Ruminococcaceae
What mainly influences adult enterotypes?
Long-term diet
How fast does an adult gut microbiome enterotype change after a diet change?
Very slowly; it is relatively stable
If a Bacteroides-dominant person becomes vegan for 2 weeks, what happens to their enterotype?
It stays Bacteroides
Why would 2 weeks of veganism not shift a Bacteroides enterotype to Prevotella?
Enterotypes are linked to long-term diet and are relatively stable
Are enterotypes sharply separate categories?
No, they overlap
Does having one enterotype mean you completely lack the other groups?
No, it just means one group is more dominant
Which enterotype is associated with long-term vegetarian diets?
Prevotella
Do enterotypes themselves automatically indicate health vs disease?
No, they mainly describe community composition
What kind of compounds can gut microbes produce besides SCFAs?
Antibiotics, antioxidants, neurotransmitters, neuromodulators, and immunomodulators
What does Ruminococcus gnavus produce that was highlighted in lecture?
Ruminococcin A, Ruminococcin C, and tryptamine
What are Ruminococcin A and C?
Antibiotic compounds
What is tryptamine in this context?
A neurotransmitter produced by gut microbes
What does Clostridium sporogenes produce that was mentioned?
Indolepropionic acid
What is indolepropionic acid?
A protective antioxidant
Which compound listed had an undefined producer but neuromodulatory activity?
4-Ethylphenylsulfate
Which Bacteroides product was highlighted as immunomodulatory?
Propionic acid
Which Bacteroides fragilis product was highlighted as immunomodulatory?
Polysaccharide A
What broad body systems can the gut microbiome influence?
Digestion, immunity, and the nervous system
What important nutrients can the gut microbiome help produce?
Certain vitamins such as vitamin K, riboflavin, and vitamin B12
Why are gut microbes important for digestion?
Humans are poorly equipped to digest many complex carbohydrates on their own
Which carbohydrates can humans digest relatively well?
Some starch, lactose, and sucrose
What happens to most other complex carbohydrates we eat?
They must be digested by intestinal symbionts
Where are the microbes that help most with complex carbohydrate digestion?
The distal small intestine and colon, especially the colon
What do gut microbes do with complex carbohydrates?
They ferment them to short-chain fatty acids
What is the relationship between fiber and gut microbes?
Fiber feeds gut microbes, which convert it into useful metabolites like SCFAs
Why is fiber important according to this lecture?
Humans rely on microbial fermentation of complex carbohydrates for important gut benefits
Which bacterial genus was emphasized as excellent at degrading glycans?
Bacteroides
What are glycans?
Complex carbohydrate structures from diet or mucus
What are PULs?
Polysaccharide utilization loci
What do PULs do?
They encode functions involved in breaking down complex carbohydrates
Why are Bacteroides notable genomically?
A large portion of their genome is dedicated to glycan degradation
About how much of Bacteroides genes were said to be dedicated to glycan degradation?
About 18–20%
How does the human genome compare with Bacteroides for glycan-degrading enzymes?
Humans encode about 99, while Bacteroides have more than 250 each
What does this enzyme difference tell you?
Gut microbes greatly expand our carbohydrate-digesting capacity
What is the termite analogy meant to show?
Like termites rely on microbes to digest cellulose, humans rely on gut microbes to digest many complex carbs
What is a probiotic?
A live microorganism promoted as giving a health benefit
What is a prebiotic?
A compound in food that promotes growth or activity of beneficial microbes
Are probiotics and prebiotics the same thing?
No
What is an example of a prebiotic from this lecture?
Human milk oligosaccharides
Why should you be cautious about probiotic claims?
Many popular claims are not strongly substantiated
What is the simplest exam logic chain for infant gut health?
HMOs feed Bifidobacteria, Bifidobacteria make SCFAs, SCFAs support gut cells, defense, and immune balance