Microbiology Exam 3: Basics to Medical Reasoning

Comprehensive vocabulary flashcards covering microbial pathogenicity, epidemiology, innate immunity, adaptive immunity, and infections of the skin, eyes, and respiratory system based on Chapters 15, 16, 17, 18, 21, and 22.

Sign

An objective and measurable indication of disease, such as a measured body temperature in fever.

Symptom

A subjective experience of disease felt and reported by the patient, such as nausea, muscle aches, or headache.

Communicable Disease

An infectious disease capable of spreading from one host to another.

Contagious Disease

A communicable disease that is easily and readily transmissible from person to person.

Noncommunicable Infectious Disease

An infectious disease acquired without ordinary person-to-person spread, such as tetanus caused by environmental Clostridium tetani spores entering a wound.

Iatrogenic Disease

A disease or infection directly caused by a medical procedure, such as introducing resident oral bacteria into the bloodstream during dental work.

Healthcare-Associated Infection (HAI)

An infection acquired in a healthcare delivery setting, such as a hospital or clinic, also termed a nosocomial infection.

Prodromal Period

The second stage of an acute infectious disease where the pathogen continues to multiply and the host begins experiencing vague, nonspecific early signs and symptoms.

Opportunistic Pathogen

An organism that typically resides as a commensal or low-virulence microbe but causes disease when host defenses are weakened or when it gains access to an inappropriate body site.

$\text{ID}_{50}$ (Median Infectious Dose)

The number of pathogen cells or virions required to establish active infection in $50\%$ of an exposed test group under stated experimental conditions.

$\text{LD}_{50}$ (Median Lethal Dose)

The dose of pathogen cells, virions, or toxin required to kill $50\%$ of an exposed test group under stated experimental conditions.

Molecular Koch's Postulates

A causal framework where a candidate virulence gene is identified in a virulent strain, disrupted to demonstrate loss of virulence, and reintroduced to verify restoration of the virulent phenotype.

Focal Infection

An infection where a pathogen or toxin from a localized primary focus spreads through the bloodstream or lymph to seed infection at a secondary body site.

Adhesin

A surface protein or carbohydrate structure on a pathogen that specifically binds to matching host cell receptors, facilitating colonization and resisting mechanical removal.

Hyaluronidase

An exoenzyme virulence factor that degrades hyaluronic acid in extracellular matrix materials, acting as a spreading factor to facilitate tissue invasion.

Exotoxin

A soluble, highly potent protein toxin produced and secreted by certain Gram-positive or Gram-negative bacteria, typically heat-sensitive with specific cellular targets.

Endotoxin

The lipid A moiety of lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria, which is heat-stable and released during cell lysis to trigger excessive host inflammation.

Superantigen

A bacterial exotoxin that bridges MHC II and T-cell receptors (TCR) outside the normal antigen groove, driving massive, nonspecific polyclonal T-cell activation and excessive cytokine release.

Incidence

The number of new cases of a disease arising in a defined population at risk during a specified time interval.

Prevalence

The total number or proportion of individuals with an existing disease in a defined population at a specific point in time or over a defined period.

Morbidity Rate

The proportion or rate of individuals in a specified population suffering from illness or disease during a defined period.

Mortality Rate

The proportion or rate of deaths in a defined population resulting from a specific disease over a defined time interval.

Sporadic Disease

A disease that occurs only occasionally, unpredictably, and in scattered isolated geographic cases without a persistent baseline presence.

Endemic Disease

A disease that maintains a constant, expected baseline presence at a steady frequency within a particular geographic region or population.

Epidemic

An occurrence of disease cases in a given population or region that is clearly in excess of normal baseline expectancy.

Pandemic

An epidemic that has spread over multiple countries, continents, or worldwide, affecting a substantial proportion of the global population.

Fomite

An inanimate object, such as a contaminated blanket, doorknob, or medical instrument, that transfers an infectious agent between hosts.

Biological Vector

A living animal host, commonly an arthropod, in which a pathogen develops or multiplies as part of its life cycle before transmission to another host.

Mechanical Vector

A living animal that physically carries an infectious agent from one surface to another without being infected or serving as a site for microbial multiplication.

Vehicle Transmission

The transmission of pathogens through contaminated inanimate reservoirs such as food, water, or air.

Point-Source Outbreak

A type of common-source epidemic where exposure to the infectious vehicle occurs in a single, brief event, causing cases to cluster within a narrow time window.

Propagated Outbreak

An outbreak sustained by direct host-to-host spread in successive generations of transmission without reliance on a single common exposure source.

Mucociliary Escalator

A mechanical respiratory defense where goblet cells secrete mucus to trap inhaled debris, and coordinated ciliated epithelial cells sweep the mucus upward to the pharynx for removal.

Lysozyme

An innate antibacterial chemical enzyme present in tears, saliva, and mucus that cleaves the glycosidic bonds connecting NAG and NAM in peptidoglycan.

Antimicrobial Peptides (AMPs)

Host-secreted chemical defense peptides, including defensins and dermcidin, that kill or inhibit microbes by disrupting their cellular membranes.

Bacteriocins

Antimicrobial protein products produced by resident microbiota that inhibit or kill competing bacterial species, contributing to colonization resistance.

Multipotent Hematopoietic Stem Cell

The undifferentiated precursor stem cell residing in the bone marrow that gives rise to all erythrocytes, leukocytes, and thrombocytes through hematopoiesis.

Neutrophil

The most abundant circulating polymorphonuclear leukocyte (PMN) in healthy adults, acting as an early phagocytic responder that uses granules and NETs to destroy microbes.

Macrophage

A large tissue-resident phagocyte derived from circulating monocytes that ingests microbes, produces inflammatory cytokines, and presents processed antigen to helper T cells.

Natural Killer (NK) Cell

An innate lymphoid cell that destroys infected or abnormal host cells by detecting reduced surface MHC I expression and releasing cytotoxic perforin and granzymes to induce apoptosis.

Pathogen-Associated Molecular Patterns (PAMPs)

Conserved molecular structures shared across classes of microbes (such as peptidoglycan, flagellin, and lipopolysaccharide) that are recognized by innate host receptors.

Pattern-Recognition Receptors (PRRs)

Host cell receptors, including Toll-like receptors (TLRs), that recognize microbial PAMPs to activate innate defensive and inflammatory signaling cascades.

Extravasation (Diapedesis)

The directional transit of leukocytes across activated vascular endothelium from the bloodstream into surrounding inflamed tissues.

Opsonization

The coating of a pathogen with immune proteins known as opsonins, such as complement factor $C3b$ or antibody $IgG$, to enhance binding and phagocytosis.

Membrane Attack Complex (MAC)

A pore-forming assembly of complement proteins ($C5b$, $C6$, $C7$, $C8$, and polymerized $C9$) that inserts into target microbial membranes, inducing osmotic lysis.

Granuloma

A localized, organized collection of macrophages, epithelioid cells, multinucleated giant cells, and lymphocytes formed to isolate and contain a persistent inflammatory or infectious stimulus.

Pyrogen

A fever-inducing agent—either exogenous like bacterial LPS or endogenous like IL-1, IL-6, and TNF—that prompts the hypothalamus to elevate the thermoregulatory set point via prostaglandin $\text{PGE}_2$.

Sepsis

A life-threatening condition marked by infection-associated organ dysfunction triggered by a dysregulated, excessive systemic host immune response.

Epitope

A specific, distinct molecular feature on an antigen molecule that is directly bound by an antigen-specific B-cell receptor, T-cell receptor, or antibody.

Hapten

A small foreign molecule that can be recognized by antibodies but is not immunogenic on its own unless covalently coupled to a larger carrier protein.

Fab Region

The antigen-binding fragment of an antibody monomer composed of the variable domains of one heavy chain and one light chain that define epitope binding specificity.

Fc Region

The crystallizable fragment composed of heavy-chain constant domains of an antibody that binds to complement components and Fc receptors on effector immune cells.

$$\text{IgM}$$

The initial antibody class secreted during a primary immune response, existing as a monomeric B-cell receptor and secreted as a high-avidity pentamer.

$$\text{IgG}$$

The principal antibody class in serum and extravascular fluids that efficiently opsonizes pathogens, crosses the placenta to confer passive neonatal immunity, and dominates the secondary response.

$$\text{IgA}$$

The primary antibody class found in mucosal secretions, saliva, tears, and breast milk, typically assembled as a secretory dimer to prevent microbial attachment to mucosal surfaces.

$$\text{IgE}$$

The antibody class that binds tightly via its Fc region to receptors on mast cells and basophils, mediating type I hypersensitivity and extracellular defenses against parasitic worms.

Major Histocompatibility Complex Class I (MHC I)

A surface glycoprotein heterodimer composed of an alpha chain and $\beta_2\text{-microglobulin}$, expressed on nearly all nucleated host cells, presenting proteasome-processed endogenous peptides to $\text{CD8}^+$ T cells.

Major Histocompatibility Complex Class II (MHC II)

A surface heterodimer of alpha and beta chains expressed exclusively on professional antigen-presenting cells (dendritic cells, macrophages, B cells), presenting endosomal-processed exogenous peptides to $\text{CD4}^+$ T cells.

Cytotoxic T Lymphocyte (CTL)

An activated $\text{CD8}^+$ effector T cell that recognizes matching foreign peptide presented on MHC I and induces apoptotic target-cell death via perforin and granzymes.

Antibody-Dependent Cellular Cytotoxicity (ADCC)

An immune defense process in which target cells or parasites are coated by specific antibodies and subsequently destroyed by effector cells (such as NK cells or eosinophils) binding the exposed Fc regions.

Class Switching

A biological mechanism in activated B cells that replaces the constant region of the antibody heavy chain to change the antibody class while maintaining identical antigen specificity.

Affinity Maturation

The process occurring in germinal centers where hypermutation and antigen-driven selection generate B-cell clones producing antibodies with progressively higher affinity for a given antigen.

Natural Active Immunity

Adaptive immunity and antigen-specific immunological memory developed following recovery from an actual natural infection.

Artificial Passive Immunity

Immediate, short-term immune protection acquired through medical injection of preformed antibodies, such as convalescent plasma, antivenom, or immune globulins.

Toxoid Vaccine

A vaccine formulation containing an inactivated bacterial exotoxin that elicits neutralizing antitoxin antibodies without causing toxin-mediated damage.

Live Attenuated Vaccine

A vaccine containing a viable, weakened version of a pathogen that replicates to a limited extent in the host, providing broad, durable cellular and humoral immunity.

Stratum Corneum

The outermost layer of the epidermis, composed of dead, keratinized cells that form a tough physical barrier and continuously shed to eliminate attached microbes.

Purulent

A descriptive clinical term for exudates containing pus, which is an accumulation of dead leukocytes (mainly neutrophils), microbes, and cellular debris.

Mannitol Salt Agar (MSA)

A selective and differential culture medium containing $7.5\%$ sodium chloride to isolate halotolerant staphylococci, and mannitol with phenol red to identify mannitol fermentation (yellow color change).

Protein A

A surface virulence protein of Staphylococcus aureus that binds the Fc region of $\text{IgG}$ in reverse orientation, impeding opsonophagocytic clearance.

M Protein

A major fibrillar cell-wall virulence factor of Streptococcus pyogenes that inhibits complement activation and helps the bacterium resist phagocytosis.

Necrotizing Fasciitis

A rapidly spreading, life-threatening infection of the subcutaneous fascia and tissue, frequently associated with Streptococcus pyogenes, requiring immediate surgical debridement and systemic antimicrobial therapy.

Trachoma

A chronic conjunctival infection caused by Chlamydia trachomatis serovars A, B, Ba, and C that causes eyelid scarring, inward turned eyelashes (trichiasis), and corneal blindness.

Herpetic Keratitis

A vision-threatening corneal infection caused by Herpes simplex virus 1 (HSV-1) reactivation, leading to corneal inflammation and potential scarring.

Roseola Infantum

A benign childhood viral syndrome caused by Human herpesvirus 6 (HHV-6B) or HHV-7, characterized by a sudden high fever followed by an erythematous maculopapular rash appearing as the fever resolves.

Fifth Disease (Erythema Infectiosum)

A mild viral infection caused by Parvovirus B19 that infects erythroid precursors, clinically marked by a distinctive 'slapped-cheek' facial rash followed by a lacy macular rash.

Dermatophyte

A fungus belonging to the genera Trichophyton, Microsporum, or Epidermophyton that consumes keratin as a nutrient to infect skin, hair, or nails.

Sporotrichosis

A subcutaneous mycosis caused by traumatic skin puncture with Sporothrix schenckii from plants (e.g., rose thorns), creating ulcerated nodules along draining lymphatic vessels.

Acanthamoeba Keratitis

A severe, difficult-to-treat corneal infection caused by the free-living amoeba Acanthamoeba, strongly associated with wearing contact lenses while swimming or using nonsterile water.

Loiasis

A filarial nematode infection caused by Loa loa, transmitted by Chrysops deerflies, characterized by transient Calabar swellings and adult worms migrating under the conjunctiva.

Epiglottis

A cartilaginous flap above the larynx that folds over the trachea during swallowing, serving as the anatomical dividing landmark between the upper and lower respiratory tracts.

Diphtheria Toxin

An A-B exotoxin produced by toxigenic Corynebacterium diphtheriae that ADP-ribosylates host elongation factor 2 (EF-2), halting protein synthesis and forming a thick pseudomembrane in the throat.

Quellung Reaction

A serological diagnostic test where specific anticapsular antibodies bind to the capsule of Streptococcus pneumoniae, causing the capsule to appear swollen under microscopic examination.

Walking Pneumonia

A clinical term for milder atypical bacterial pneumonia frequently caused by Mycoplasma pneumoniae, an organism lacking a peptidoglycan cell wall and thus intrinsically resistant to beta-lactams.

Catarrhal Stage

The initial, highly contagious stage of pertussis (whooping cough) characterized by mild, nonspecific upper respiratory symptoms resembling a common cold.

Paroxysmal Stage

The second stage of pertussis characterized by repeated severe coughing spasms followed by a characteristic whooping sound on inspiration, driven by tracheal cytotoxin-induced damage to ciliated cells.

Ghon Complex

A pathological hallmark of primary pulmonary tuberculosis consisting of a primary parenchymal lung lesion (Ghon focus) combined with granulomatous infection in draining hilar lymph nodes.

Latent Tuberculosis Infection (LTBI)

A contained infection where Mycobacterium tuberculosis survives within cellular lung granulomas without producing symptoms, active disease, or infectious transmission to others.

Mantoux Tuberculin Skin Test (TST)

A diagnostic screening test for mycobacterial exposure measuring delayed-type hypersensitivity induration (firmness) in millimeters $48\text{--}72\,\text{hours}$ after intradermal injection of PPD.

Interferon-Gamma Release Assay (IGRA)

A blood test measuring host T-cell production of interferon-gamma in response to Mycobacterium tuberculosis-specific antigens, which does not produce false-positive results from prior BCG vaccination.

Antigenic Drift

Minor, gradual antigenic alterations in the hemagglutinin and neuraminidase proteins of influenza viruses caused by accumulated point mutations during viral replication.

Antigenic Shift

A sudden, major antigenic change occurring in influenza A viruses when two different viral strains coinfect the same host cell and reassort their segmented RNA genomes.

Koplik Spots

Small, red oral mucosal lesions with white or bluish centers that appear inside the cheeks as an early diagnostic pathognomonic sign of measles (rubeola).

Syncytium

A large multinucleated cell formed by the fusion of adjacent host plasma membranes, characteristic of the cytopathology produced by respiratory syncytial virus (RSV).

Coccidioidomycosis

An endemic pulmonary fungal infection ('Valley fever') acquired by inhaling arthroconidia from desert soils of the southwestern United States, which develop into endospore-filled spherules in tissue.

Aspergilloma

A tangled ball of Aspergillus fungal hyphae, cellular debris, and fibrin that colonizes and grows within a preexisting pulmonary cavity.

Pneumocystis Pneumonia (PCP)

An opportunistic fungal pneumonia caused by Pneumocystis jirovecii in severely immunocompromised individuals, uniquely transmissible through airborne droplets between individuals and treated with TMP-SMX.