Microbiology Ch 33 Human Microbiota

What is a "holobiont"?

An assemblage of a host and the many other species living in or around it, which together form a discrete ecological unit.

What is the estimated ratio of bacterial cells to human cells in a 70kg adult?

Roughly 1:1 to 3:1 (approx. 3.8e13 bacteria to 3.0e13 human cells).

Name three beneficial effects of normal microbiota.

Produce vitamins (K and B12), educate the immune system, and occupy niches to prevent pathogen colonization.

What is "colonization resistance"?

The mechanism by which the normal microbiota protects the host against invasion by new, potentially pathogenic microbes.

What is "microbial endocrinology"?

The study of how microbes can impact host behavior, neural development, and hormone levels.

Define "normal human microbiota".

Microorganisms commonly associated with the human body, usually in a symbiotic relationship.

What are "transient" microbes?

Microbes that are present temporarily but do not establish a permanent residence on the host.

What is the "Human Microbiome Project" (HMP)?

An initiative to characterize the microbial communities found at several different sites on the human body.

How does a newborn first acquire their microbiome?

Through the birth canal (vaginal delivery) or skin contact (C-section), followed by feeding and environmental exposure.

Which genus of bacteria is dominant in the bifidogenic environment of breastfed infants?

Bifidobacterium.

What is the function of "Bifidobacteria" in infants?

They can synthesize all amino acids and growth factors from simple carbohydrates and help surface-coat the gut to prevent pathogen attachment.

Define "dysbiosis".

An imbalance in the microbial community that is associated with disease or poor health.

What are the three main microenvironments of the skin?

Dry (forearm), Moist (underarm/groin), and Oily/Sebaceous (face/upper back).

Which bacterium is commonly associated with acne?

Cutibacterium acnes (formerly Propionibacterium).

Why is the skin an inhospitable environment for many microbes?

It has a slightly acidic pH, high salt concentration, and contains inhibitory substances like lysozyme.

What is the "mucociliary blanket"?

A layer of mucus in the respiratory tract that traps microbes and is moved toward the mouth by ciliated epithelial cells.

Which part of the respiratory tract is usually sterile or contains very few microbes?

The lower respiratory tract (lungs).

How does the eye limit bacterial growth?

Through the flushing action of tears and the presence of lysozyme in the lacrimal fluid.

What is the "primary colonizer" of the teeth?

Streptococcus mutans (and other S. sanguis types).

How does the stomach inhibit microbial growth?

Through its extremely low pH (approx. 2.0).

Which part of the small intestine has the highest concentration of microbes?

The ileum (the distal portion).

What is the "anaerobic" nature of the large intestine?

The colon is strictly anaerobic, supporting a massive population of obligate anaerobes like Bacteroides.

What are "Short Chain Fatty Acids" (SCFAs)?

Byproducts of fiber fermentation by gut bacteria (like butyrate) that provide energy for colon cells.

Define a "biofilm".

A complex, slime-encased community of microbes adhering to a surface.

What is the "Extracellular Polymeric Substance" (EPS)?

The "matrix" or "slime" made of polysaccharides, proteins, and DNA that holds a biofilm together.

What are the five stages of biofilm formation?

Reversible attachment, Irreversible attachment, Maturation I, Maturation II, and Dispersion.

What is "quorum sensing"?

The process where bacterial cells communicate via chemical signals to coordinate behavior based on population density.

What is an "autoinducer"?

A signaling molecule secreted by bacteria in quorum sensing (e.g., Acyl-homoserine lactones or AHLs).

Why are biofilms clinically significant?

They are highly resistant to antibiotics and immune responses, often forming on medical implants.

What is "heterogeneity" in a biofilm?

The presence of different metabolic states and species within the same biofilm structure.

Define "probiotics" according to the WHO.

Live microorganisms which, when administered in adequate amounts, confer a health benefit to the host.

Who is Elie Metchnikoff?

A Nobel laureate who first hypothesized that yogurt-consuming Balkan populations lived longer due to gut bacteria.

What is "Lactobacillus rhamnosus GG" (LGG)?

A well-studied probiotic strain known for promoting mucin production and stabilizing gut populations.

What is a "prebiotic"?

Non-digestible food ingredients (like fiber) that stimulate the growth and/or activity of beneficial bacteria.

What is a "synbiotic"?

A product that contains both probiotics and prebiotics.

What is the "gut-brain axis"?

The bidirectional communication link between the central nervous system and the enteric nervous system, often mediated by microbes.

Which gas produced by gut bacteria is often associated with "egg-smelling" flatulence?

Hydrogen sulfide (H2S).

Name a vitamin produced by E. coli in the human colon.

Vitamin K.

How does "Bacteroides thetaiotaomicron" help the host?

It breaks down complex plant polysaccharides that human enzymes cannot digest.

What is the "acid mantle" of the skin?

The thin, slightly acidic film on the surface of human skin that acts as a barrier to bacteria.

What is "detachment" or "dispersion" in a biofilm?

The stage where pieces of the biofilm or individual cells break off to colonize new surfaces.

What is "intercellular signaling"?

Communication between different cells, crucial for the maturation of a biofilm.

What is "bioremediation"?

The use of microbes (often in biofilms) to clean up contaminated environments like oil spills.

What is "dental plaque"?

A naturally occurring biofilm on the surface of teeth.

Which bacterium is famous for colonizing the stomach and causing ulcers?

Helicobacter pylori.

What is "mucin"?

A glycoprotein constituent of mucus that probiotics like LGG can stimulate.

How do probiotics contribute to "immunomodulation"?

By stimulating the production of anti-inflammatory cytokines or strengthening the gut barrier.

What is "fecal microbiota transplantation" (FMT)?

A procedure where fecal matter from a healthy donor is placed into the colon of a patient to restore microbial balance.

For which infection is FMT a highly successful treatment?

Clostridioides difficile (C. diff).

What is "AHL" (Acyl-homoserine lactone)?

The most common signaling molecule used by Gram-negative bacteria for quorum sensing.

What is "AI-2" (Autoinducer-2)?

A signaling molecule used for inter-species communication among bacteria.

How does "flow" or "shear stress" affect a biofilm?

It influences the shape and structural integrity of the biofilm as it grows.

What is "metabolic cooperativity"?

When the waste product of one microbe in a biofilm serves as the food source for another.

What are "persister cells"?

Dormant cells within a biofilm that are highly tolerant to antibiotics without being genetically resistant.

Why do antibiotics often fail against biofilms?

Slow penetration of the matrix, altered microenvironments (low pH/O2), and the presence of persister cells.

What is "Lactobacillus acidophilus"?

A common probiotic bacterium used to balance vaginal and intestinal flora.

What is "Bifidobacterium animalis"?

A probiotic often added to commercial yogurts to improve digestive regularity.

What is "opportunistic" pathogen?

A member of the normal microbiota that causes disease only when the host's defenses are compromised.

What is "sebum"?

The oily secretion of sebaceous glands that provides nutrients for skin microbiota.

Where is "Staphylococcus epidermidis" most commonly found?

On the skin; it is a major component of the normal skin microbiota.

What is "malodor" in the underarm caused by?

Bacterial breakdown of organic compounds in sweat into volatile fatty acids.

What is the "urethra" microbiota like?

The distal portion contains some microbes (e.g., S. epidermidis), but the upper urinary tract is usually sterile.

How does the female vaginal tract maintain a low pH?

Lactobacillus species ferment glycogen into lactic acid.

What is "Vaginal Dysbiosis"?

A shift from Lactobacillus dominance to a diverse mix of anaerobes, often called Bacterial Vaginosis (BV).

What is "GABA"?

A neurotransmitter that some probiotics (like LGG) can influence to reduce stress and anxiety.

What is "TNF-alpha"?

A pro-inflammatory cytokine whose production can be suppressed by certain probiotic bacteria.

What is "Propionate"?

A short-chain fatty acid produced by gut bacteria that may help regulate appetite and metabolic health.

What is "Butyrate"?

The SCFA that serves as the primary energy source for colonocytes (cells lining the colon).

What is "Acetate"?

The most abundant SCFA in the colon, involved in lipid synthesis and energy storage.

What is the "mucus layer" of the gut?

A physical barrier that prevents bacteria from coming into direct contact with intestinal epithelial cells.

What is "secretory IgA"?

An antibody secreted onto mucosal surfaces that helps regulate the composition of the microbiota.

Define "pathobiont".

A member of the normal microbiota that has the potential to cause disease under certain conditions.

What is "colonization"?

The successful occupation of a new habitat by a microorganism.

What is "adhesion"?

The process by which microbes attach to host cells or surfaces using pili, fimbriae, or capsules.

What is "metagenomics" in the context of the microbiome?

Sequencing all genetic material in a sample to identify which microbes are present and what they are doing.

What is "16S rRNA sequencing"?

A standard method for identifying and comparing bacterial species in a microbiome sample.

What is the "oral microbiome"?

The collection of microbes living in the mouth, including the teeth, tongue, and gums.

What is "biofilm architectural complexity"?

The 3D structure of a biofilm, including channels for nutrient and waste transport.

What are "water channels" in a biofilm?

Gaps in the matrix that allow for the distribution of nutrients and oxygen to deep-seated cells.

What is "bioluminescent" quorum sensing?

A phenomenon where bacteria like Aliivibrio fischeri produce light only when they reach a high population density.

What is "competence" in quorum sensing?

The ability of a cell to take up extracellular DNA, often triggered by signaling molecules.

What is "virulence factor" expression?

The production of toxins or enzymes that facilitate infection, often regulated by quorum sensing.

What is "antimicrobial peptide" (AMP) production?

A host defense mechanism where the body produces small proteins that kill bacteria.

What is "Bacteriocin" production by normal flora?

The secretion of proteins that kill closely related competing bacterial strains.

What is "metabolic syndrome"?

A group of conditions (obesity, high BP, etc.) that has been linked to changes in the gut microbiome.

What is the "hygiene hypothesis"?

The idea that a lack of early childhood exposure to microbes leads to an increase in allergies and autoimmune diseases.

What is "vertical transmission"?

The transfer of microbes from mother to child during birth.

What is "horizontal transmission"?

The spread of microbes between individuals who are not in a parent-child relationship.

What is "niche exclusion"?

The principle that two species competing for the same resources cannot coexist; the better competitor excludes the other.

How does "fiber" act as a prebiotic?

It passes undigested to the colon, where beneficial bacteria ferment it for energy.

What is "Lactococcus lactis"?

A bacterium used in cheese production that also produces the bacteriocin Nisin.

What is "Enterococcus faecalis"?

A common gut inhabitant that can become an opportunistic pathogen in hospital settings.

What is "Candida albicans"?

A fungal member of the normal microbiota that can cause yeast infections if the bacterial balance is disrupted.

What is "antibiotic-associated diarrhea"?

A condition where antibiotics kill beneficial gut bacteria, allowing pathogens like C. diff to overgrow.

What is "Saccharomyces boulardii"?

A yeast used as a probiotic to prevent and treat various types of diarrhea.

What is "colonocyte"?

An epithelial cell of the large intestine (colon).

What is "Treg" cell (Regulatory T cell)?

An immune cell that helps prevent autoimmunity and is "educated" by the gut microbiota.

What is "LPS" (Lipopolysaccharide)?

A component of Gram-negative cell walls that can trigger inflammation if it leaks into the bloodstream (leaky gut).

What is "intestinal permeability"?

Commonly called "leaky gut," it is the loss of tight junctions between gut cells, often linked to dysbiosis.

What is "microbial diversity"?

The number of different species and their relative abundance within a microbiome.