Microbiology & Immunology Comprehensive Review

84 question-and-answer flashcards summarizing key concepts from microbial symbiosis, human microbiome, innate and adaptive immunity, pathogenesis, epidemiology, vaccines, and microbial biotechnology.

What are ectosymbionts?

Organisms that live on the surface of another organism (e.g., skin microbiota).

What are endosymbionts?

Organisms that live within another organism (e.g., gut microbes).

In microbiology, what is a consortium?

A host that harbors more than one associated symbiont.

Define mutualism in microbial interactions.

An obligatory interaction in which both partners depend on each other and often undergo genomic reduction.

Which two microbial interactions are obligatory and typically show genomic reduction?

Mutualism and parasitism.

Define predation in microbial interactions.

A killing interaction in which the predator consumes or kills the prey; the predator may be larger or smaller than its prey.

Define cooperation in microbial interactions.

A non-obligatory relationship in which both partners benefit but can survive independently.

Define parasitism.

An interaction in which a parasite exploits a host for nutrients without intending to kill it.

Define commensalism.

An interaction in which one organism benefits and the other is neither harmed nor helped; often due to an environmental change.

Define amensalism.

An interaction in which one microbe harms another through the release of a chemical substance.

Define competition in microbial ecology.

When organisms vie for the same resources or coexist at lower population levels due to resource limitation.

Which microbial interactions are considered positive (beneficial) for at least one participant without harm to the other?

Cooperation, commensalism, and mutualism.

Which microbial interactions are considered negative?

Competition, amensalism, predation, and parasitism.

Which two interactions commonly lead to genomic reduction?

Mutualism and parasitism.

Give an example of cooperation in the human gut.

Escherichia coli living in the human intestine, aiding vitamin production while receiving nutrients.

How does Bdellovibrio kill its prey?

It penetrates the periplasmic space and grows between the cell wall and plasma membrane of the prey bacterium.

Must parasites kill their host to obtain nutrients?

No; parasitism exploits the host without necessarily killing it.

How do bacteriocins differ from antibiotics in amensalism?

Bacteriocins (e.g., colicins) target closely related microbes, whereas antibiotics (e.g., penicillin) target distantly related species.

What is the human microbiome?

The community of microbes that live on and in the human body, supporting digestion, immunity, and pathogen protection.

Why is the human body considered a superorganism?

Because it includes human cells plus its vast microbiome, which produces molecules like cathelicidins and contains both ecto- and endosymbionts.

List three key traits of Bifidobacteria.

They are prototrophic, probiotic, and fermentative.

What does gnotobiotic mean?

An organism reared in a sterile environment with a weakened or underdeveloped immune system.

Why is human skin inhospitable to many microbes?

Its low pH and dryness inhibit microbial growth.

How does Cutibacterium acnes contribute to acne?

Excess sebum allows the bacterium to overgrow and cause opportunistic infection and inflammation.

Where is Staphylococcus epidermidis most commonly found?

On the skin, especially near the eyes and nose.

Which portion of the gastrointestinal tract harbors the highest microbial abundance?

The large intestine, which is largely anaerobic.

Which major organs are normally sterile in healthy individuals?

Lungs and kidneys.

What is the gut-brain axis?

Bidirectional communication between gut microbes and the central nervous system, possibly via the vagus nerve (CN X) and immune mediators.

Name four diseases linked to dysbiosis of the microbiome.

Cardiovascular disease, cancer, inflammatory bowel disease, and metabolic syndrome.

Define probiotics.

Live microorganisms that confer a health benefit on the host when administered in adequate amounts.

Define prebiotics.

Non-digestible food ingredients (e.g., fiber) that selectively stimulate the growth or activity of beneficial microbes.

Define synbiotics.

Products that combine prebiotics and probiotics for synergistic health effects.

What are the three activation pathways of the complement system?

Classical, lectin, and alternative pathways.

Which complement fragments stimulate inflammation?

C3a and C5a.

What is the function of the membrane attack complex (MAC)?

It forms pores that cause cell lysis, consisting of complement proteins C5–C9.

What is opsonization and which complement fragment mediates it?

Coating of pathogens to enhance phagocytosis; mediated primarily by C3b.

What are leukocytes?

White blood cells involved in innate and adaptive immune responses.

Name six major types of leukocytes.

Monocytes, macrophages, granulocytes, mast cells, lymphocytes, and dendritic cells.

True or false: All lymphocytes are leukocytes, but not all leukocytes are lymphocytes.

True.

What is the main function of basophils?

Participation in allergic and hypersensitivity reactions (they stain bluish-black).

What is the main function of eosinophils?

Defense against parasites and contribution to allergic responses (they stain red).

Why are neutrophils called "professional" phagocytes?

They are highly phagocytic, stain at neutral pH, and form pus upon death (pyogenic).

Differentiate monocytes from macrophages.

Monocytes circulate in blood and are smaller; macrophages reside in tissues and are larger and more phagocytic.

Which three cells are considered professional phagocytes?

Macrophages, neutrophils, and dendritic cells.

Where do B and T lymphocytes mature?

B cells in bone marrow; T cells in the thymus (primary lymphoid tissues).

What are M cells and where are they located?

Microfold cells in mucosa-associated lymphoid tissue (MALT) that sample gut lumen antigens.

What is a MAMP (PAMP)?

A microbe-associated molecular pattern such as LPS or flagellin recognized by the innate immune system.

What are Toll-like receptors (TLRs)?

Pattern-recognition receptors on immune cells that detect MAMPs and trigger cytokine release.

State the three main functions of adaptive immunity.

Recognize non-self, respond to non-self, and remember non-self for faster future responses.

Describe the maturation and primary role of B cells.

They mature in bone marrow, differentiate into plasma cells, and mediate humoral immunity by secreting antibodies.

Describe the maturation and primary role of T cells.

They mature in the thymus, secrete cytokines, and mediate cellular immunity as helper or cytotoxic cells.

List four traits common to both B and T cells.

CD34+ origin, classification as lymphocytes/leukocytes, activation in secondary lymphoid tissue, and ability to form memory cells.

Give an example of natural passive immunity.

Transfer of maternal antibodies to a fetus via the placenta.

Which MHC class presents endogenous antigens to CD8+ T cells?

MHC class I.

Which MHC class presents exogenous antigens to CD4+ T helper cells?

MHC class II.

Do erythrocytes express MHC I molecules?

No; they are anucleate and lack MHC I.

Name three professional antigen-presenting cells (APCs).

Dendritic cells, macrophages, and B cells.

What costimulatory molecule on APCs is required for T-helper cell activation?

B7 (binding to CD28 on T cells).

Why does T-cell production decline with age?

The thymus gradually atrophies, reducing new T-cell maturation.

What is the main function of cytotoxic T cells?

They kill infected or cancerous cells by releasing perforin and granzymes.

What is the role of regulatory T cells?

Suppress immune responses to maintain tolerance and prevent autoimmunity.

What are superantigens?

Exotoxins that non-specifically activate many T cells, causing massive cytokine release and inflammation.

Which enzyme cleaves antibodies into two Fab and one Fc fragment?

Papain.

Which antibody class is produced first during a primary immune response?

IgM.

Which antibody class can cross the placenta?

IgG.

How many IgM molecules are required to activate the classical complement pathway?

One IgM pentamer.

Where is IgA predominantly found?

Secretions such as saliva, tears, breast milk, and mucosal surfaces (MALT).

What is the primary role of IgE?

Defense against parasites and mediation of allergic reactions.

During a secondary immune response, which antibody class predominates?

IgG (with higher affinity).

What is antibody neutralization?

Antibodies bind to pathogens or toxins, blocking their attachment or activity.

What is severe combined immunodeficiency (SCID)?

A primary immunodeficiency caused by genetic defects that impair both B- and T-cell function.

What laboratory criterion defines progression to AIDS in HIV-infected patients?

A CD4+ T-cell count below 200 cells per microliter of blood.

Differentiate pathogen, infection, and disease.

Pathogen: agent that can cause disease; Infection: growth of a pathogen in/on a host; Disease: deviation from health impairing normal function.

What is tropism in infectious disease?

A pathogen’s preference for specific cell types, tissues, or hosts.

What are pathogenicity islands?

Large segments of DNA that encode clusters of virulence factors in pathogens.

What is the action of hyaluronidase?

It degrades hyaluronic acid, the "cell cement," allowing pathogen spread through tissues.

How do exotoxins differ from endotoxins in heat stability?

Exotoxins are generally heat-labile, whereas endotoxins (LPS) are heat-stable.

What is the mechanism of diphtheria toxin?

It ADP-ribosylates elongation factor-2 (EF-2), halting protein synthesis.

How does Trypanosoma brucei evade the immune system?

By antigenic variation of its variable surface glycoprotein (VSG).

Who traced a cholera outbreak in London and is called the father of modern epidemiology?

John Snow.

What is a major advantage of live attenuated vaccines?

They induce strong, long-lasting immunity with fewer boosters.

Differentiate primary and secondary metabolites in microorganisms.

Primary metabolites are essential for growth (e.g., ethanol during fermentation); secondary metabolites have ecological roles like defense (e.g., penicillin).

What agricultural role does Bacillus thuringiensis (Bt) play?

It produces insecticidal toxins used as biopesticides that target insect larvae without harming humans.

How can engineered bacteria enhance MRI imaging?

They can produce magnetosomes, serving as natural contrast agents for better image resolution.

IgM

Agglutination and activates complement

IgA

Secrets tears, saliva, breast milk, MALT

IgE

Elevated in parasitic infection and allergic reactions, opsonization