week 11 Flashcards
Which of the following statements about the human microbiome is MOST accurate?
A) The human microbiome is fully developed at birth and remains stable throughout life.
B) Each individual has a unique microbiome that is formed within the first three years of life.
C) The microbiome is highly variable within an individual and does not show stable patterns.
D) The microbiome is identical across different body sites due to uniform environmental exposure.
Each individual has a unique microbiome that is formed within the first three years of life.
Rationale: The microbiome is unique to each person and develops early in life. While it is subject to changes, it remains relatively stable unless disturbed. Different body sites have distinct microbial compositions.
Why is the human microbiome generally stable over time?
A) Microbiomes are genetically determined and do not change in response to external factors.
B) The immune system actively eliminates any new microbes, preventing changes in composition.
C) Dynamic relationships between microbes and host factors create a stable and balanced system.
D) Microbiomes cannot recover from disturbances and remain permanently altered when disrupted.
Dynamic relationships between microbes and host factors create a stable and balanced system.
Rationale: The microbiome is stable because of complex interactions between microbes, host immune responses, and environmental factors. While it can respond to disturbances, it typically returns to its original state once the disturbance is removed.
The gut microbiome produces short-chain fatty acids (SCFAs). Which of the following functions is incorrectly matched with the respective SCFA?
A) Butyrate – Increases beta-oxidation and represses glycolysis.
B) Propionate – Enhances adaptive immune system T-cell activity.
C) Acetate – Increases inflammation in colitis, arthritis, and asthma.
D) SCFAs – Serve as an energy source for intestinal cells.
Acetate helps reduce inflammation associated with conditions like colitis, arthritis, and asthma, rather than increasing it. SCFAs play multiple roles in metabolism, immunity, and gut barrier function.
Acetate – Increases inflammation in colitis, arthritis, and asthma.
Which of the following best explains the relationship between human milk oligosaccharides (HMOs) and infant microbiomes?
A) HMOs serve as a direct energy source for infants.
B) HMOs promote the growth of Bifidobacterium, which outcompetes other microbes.
C) HMOs provide essential fatty acids needed for infant brain development.
D) HMOs are metabolized by most gut bacteria, leading to increased microbial diversity.
HMOs promote the growth of Bifidobacterium, which outcompetes other microbes.
Rationale: HMOs are indigestible by humans and most bacteria, but they selectively support Bifidobacterium, shaping early gut microbiome composition.
Which of the following factors plays the MOST significant role in determining an infant’s initial gut microbiome composition?
A) The mother’s dietary habits during pregnancy
B) The method of delivery at birth
C) The infant’s exposure to solid food at six months
D) The presence of pets in the household
The method of delivery at birth
Rationale: The initial gut microbiome is influenced primarily by birth mode, with vaginally delivered infants acquiring microbes from the birth canal, while C-section-delivered infants have a microbiome more similar to skin microbiota.
What is a key limitation in microbiome research?
A) Taxonomic classification provides detailed insights into bacterial function.
B) Enzyme class information directly predicts microbial community outcomes.
C) Mice models are an accurate representation of human microbiomes.
D) Correlation in microbiome studies does not establish causation.
Correlation in microbiome studies does not establish causation.
Rationale: A major limitation in microbiome research is that correlation does not imply causation, making it difficult to determine the direct effects of microbiome changes on health outcomes.
Which of the following best describes the functional genomics approach in microbiome studies?
A) Identifying bacterial species within a sample using 16S rRNA sequencing
B) Categorizing bacterial genes by their metabolic pathways using KEGG databases
C) Using microscopy to visualize bacterial communities in different body sites
D) Classifying bacteria based on Gram staining characteristics
Functional genomics focuses on understanding gene function and interactions. KEGG categorizes enzymes by metabolic pathways, helping to predict microbial activities.
What role do fiber and complex carbohydrates play in gut microbiome health?
A) They are directly absorbed by human intestinal cells without microbial involvement.
B) They promote the growth of gut bacteria that ferment them into SCFAs.
C) They suppress the activity of microbes in the distal gut to prevent overgrowth.
D) They primarily serve as an energy source for human digestion rather than for microbes
Humans lack enzymes to digest many complex carbohydrates, so gut bacteria ferment them into SCFAs, which provide energy and regulatory benefits.
hey promote the growth of gut bacteria that ferment them into SCFAs.
How do Bacillus species inhibit quorum sensing in Staphylococcus aureus?
A) By producing lysozyme, which breaks down bacterial cell walls
B) By releasing fengycin, which blocks quorum-sensing receptor ArgC
C) By competing for nutrients and outcompeting S. aureus
D) By altering the pH to make the environment inhospitable for S. aureus
Bacillus species produce fengycin, which inhibits ArgC, preventing S. aureus (a harmful bacteria) from sensing population density and expressing virulence genes.
By releasing fengycin, which blocks quorum-sensing receptor ArgC
Why is the vaginal microbiome predominantly composed of Lactobacillus species?
A) Lactobacillus species thrive in high-oxygen environments, which dominate the vagina.
B) Lactobacillus species produce lactic acid, maintaining an acidic pH that inhibits pathogens.
C) The vaginal microbiome is highly unstable and frequently shifts to favor Lactobacillus.
D) Lactobacillus species degrade HMOs, which are abundant in the vaginal environment.
The vaginal microbiome remains stable due to the dominance of Lactobacillus, which produces lactic acid, creating an acidic environment that prevents pathogen overgrowth.
Lactobacillus species produce lactic acid, maintaining an acidic pH that inhibits pathogens.
Why does taxonomic classification alone provide little information about microbiome function?
A) Bacteria of the same species always have identical metabolic functions.
B) Different bacterial species can perform the same metabolic functions, making taxonomy insufficient.
C) Taxonomy describes only bacterial shape and size, which are unrelated to function.
D) Microbiome function is determined exclusively by the host, not by microbial composition.
Answer: B) Different bacterial species can perform the same metabolic functions, making taxonomy insufficient.
Taxonomic classification groups bacteria based on genetic relationships, but function depends on gene expression and metabolic pathways. Different species can contribute to similar functions, meaning taxonomy alone does not predict microbiome activity.
Why can we not make conclusions based on correlation in microbiome studies?
A) Correlations only describe associations and do not prove a direct cause-and-effect relationship.
B) All observed microbiome changes are always due to external interventions, not natural variation.
C) Microbiome composition is fixed, so correlations cannot change over time.
D) If a bacterial species is present in a disease state, it must be the cause of the disease.
Answer: A) Correlations only describe associations and do not prove a direct cause-and-effect relationship.
Rationale: Correlation does not imply causation—just because a bacterial species is associated with a condition does not mean it causes it. Many factors can influence microbiome composition, requiring controlled experiments to establish causal relationships.
How do probiotics affect quorum sensing?
- Probiotics produce molecules that block quorem sensing
(Bacillus species produce fengycin blocks ArgC, which prevents AIP to bind to ArgC, resulting in no quorum sensing) - probiotics outcompete pathogens and preventing quorum sensing and quickly degrade quorum sensing molecules
Why do probiotics disrupt quorum sensing to occur in other bacteria?
- they reduce the bacteria to do harm and cause infections to the human (the host)
- prevents biofilm formation (which makes it harder to treat infections)
- strengthen the gut microbiome against pathogens
What is the key difference between a probiotic and a prebiotic?
A) A probiotic is a live microorganism that benefits the host, while a prebiotic is a specific type of gut microbe that enhances digestion.
B) A probiotic is a non-digestible food component that promotes gut bacteria growth, while a prebiotic is a live microbe that improves gut health.
C) A probiotic is a live microbe that provides health benefits, while a prebiotic is a substance that feeds beneficial gut bacteria.
D) A probiotic is a type of dietary fiber that promotes gut health, while a prebiotic is a strain of bacteria that enhances nutrient absorption.
A probiotic is a live microbe that provides health benefits, while a prebiotic is a substance that feeds beneficial gut bacteria.
Rationale: Probiotics are live microorganisms (such as Bifidobacterium or Lactobacillus) that support gut health when consumed. Prebiotics are non-digestible substances (such as HMOs or fiber) that stimulate the growth of beneficial bacteria in the gut.
What are the sources of short-chain fatty acids (SCFAs) in infants and adults?
A) SCFAs in both infants and adults come from host digestive enzymes breaking down dietary fiber and HMOs.
B) SCFAs in adults primarily come from bacterial fermentation of dietary fiber, while in infants, they are mainly produced from HMO fermentation by gut microbes.
C) SCFAs in both infants and adults come mainly from the metabolism of human milk components.
D) SCFAs in adults come from microbial fermentation of proteins, whereas in infants, they are synthesized directly from milk fats.
SCFAs in adults primarily come from bacterial fermentation of dietary fiber, while in infants, they are mainly produced from HMO fermentation by gut microbes.
Rationale: In adults, SCFAs are mainly produced when gut bacteria ferment dietary fibers. In infants, SCFAs come from bacterial fermentation of HMOs (Human Milk Oligosaccharides), since dietary fiber intake is low. Host enzymes do not directly break down fiber or HMOs into SCFAs—only gut microbes perform this fermentation.
Why is dietary fiber important for a healthy gut microbiome?
A) Fiber directly nourishes gut epithelial cells, making it essential for gut health.
B) Fiber provides essential vitamins to gut bacteria, enabling them to grow and outcompete harmful microbes.
C) Fiber serves as a fermentable substrate for gut bacteria, allowing them to produce short-chain fatty acids (SCFAs) that support gut health.
D) Fiber is broken down by human digestive enzymes into monosaccharides, which gut bacteria use for energy.
Fiber serves as a fermentable substrate for gut bacteria, allowing them to produce short-chain fatty acids (SCFAs) that support gut health.
Rationale:
Fiber is indigestible by humans but can be fermented by gut bacteria, producing SCFAs like acetate, propionate, and butyrate.
SCFAs lower gut pH, regulate the immune system, and provide energy to gut cells, supporting overall gut health.
Fiber is not directly broken down by human enzymes—it requires microbial fermentation.
Why do bacterial genomes need to be complex to degrade complex carbohydrates?
A) Bacteria require multiple genes to encode a variety of enzymes that break down complex carbohydrates into fermentable substrates.
B) Bacteria must store complex carbohydrates in their genome to use them efficiently.
C) Bacteria rely on host digestive enzymes, so they require a large genome to coordinate carbohydrate metabolism with the host.
D) Bacterial genomes need to be complex to prevent the breakdown of simple sugars and prioritize complex carbohydrate fermentation.
Bacteria require multiple genes to encode a variety of enzymes that break down complex carbohydrates into fermentable substrates.
Rationale:
Complex carbohydrates, like fiber and resistant starches, require multiple enzymatic steps for breakdown.
Bacteria must have genes encoding carbohydrate-active enzymes (CAZymes), such as glycoside hydrolases and polysaccharide lyases, to process these molecules.
A diverse and complex genome allows bacteria to adapt to different carbohydrate sources, supporting microbial survival and SCFA production.
Where do babies and adults recieve SCFA’s?
Babies get them from mommy’s milk
Adults get them from dietary fibre
What happens to a microbiome when an infant stops consuming breastmilk?
The infants microbiome switches to compositions that are in an adult microbiome
