Microbiology: Viruses, Bacteria, and Archaea

Comprehensive vocabulary flashcards covering the structure, replication, immune responses, and laboratory techniques associated with viruses, bacteria, and archaea.

Interferon (IF)

A protective protein produced in white blood cells, connective tissue, and the immune system following infection that exits the host cell to warn neighboring cells, inducing them to synthesize antiviral proteins and become coated against viral entry and replication.

Interleukin (IL)

A signaling protein that activates additional white blood cells and triggers flu-like symptoms, including fever, aches, and pains.

Active Immunity

Long-term immunity acquired when an organism's own immune system produces its own antibodies in response to natural infection or a vaccine.

Passive Immunity

Short-term immunity conferred by receiving pre-formed antibodies from another individual or animal serum.

Herd Immunity

A form of indirect protection from infectious disease that occurs when a sufficiently large proportion of a population is immune, limiting the spread of the pathogen and protecting unimmunized individuals.

Pathogen

A disease-causing microbe, encompassing a relatively small fraction of all existing bacteria and viruses.

Sterilization

The complete destruction of living bacteria and active viral particles using intense heat (such as boiling water) or chemical degradation.

Vector

An intermediate organism, such as a rodent, that transmits a pathogen from an infected host or reservoir to another individual.

Primary Line of Defense

Physical and chemical external barriers, including intact skin and mucus membranes, that provide broad protection against both viruses and bacteria.

Secondary Line of Defense

The non-specific internal immune response mediated by phagocytic white blood cells (macrophages) that engulf and destroy pathogens and display foreign surface antigens to T cells.

Antigen (Ag)

A specific bacterial or viral surface protein marker that is recognized as foreign and triggers an targeted immune response.

Antibody (Ab)

A specific Y-shaped protective protein synthesized by B cells that binds precisely to foreign antigens and marks the pathogen for destruction by other white blood cells.

Prophage

The latent form of a viral genome that has integrated directly into the circular chromosome of a bacterial host, replicating passively alongside host DNA during binary fission.

Capsid

The external protective protein coat enclosing the viral nucleic acid and essential enzymes.

Viral Specificity

The property whereby a given virus can only infect host cells displaying a complementary, specific surface receptor.

Retrovirus

A class of enveloped RNA viruses, such as HIV, that utilize RNA as their genetic material.

Orthomyxovirus

The family of enveloped RNA viruses responsible for influenza infections.

Lytic Cycle

A viral reproductive cycle involving attachment, penetration of viral nucleic acid, takeover of host machinery to synthesize viral components, assembly, and eventual lysis (rupture) of the host cell to release hundreds of progeny virions.

Lysogenic Cycle

A viral life cycle in which the viral nucleic acid integrates into the host genome as a dormant prophage, replicating alongside host DNA until environmental signals trigger entry into the lytic cycle.

Streak Plate Procedure

A microbiology isolation technique in which an inoculating loop is flamed, cooled, and used to spread bacteria across sequential quadrants of an agar plate to obtain isolated pure colonies.

Bacterial Lawn

A continuous, uniform layer of confluent bacterial growth covering an entire agar surface, used in antibiotic sensitivity testing.

Bioassay

A biological test that evaluates the inhibitory effectiveness of antimicrobial substances, such as antibiotic discs placed on a bacterial lawn to measure clear zones of inhibition.

Bioremediation

The environmental application of bacteria to metabolize, degrade, and neutralize toxic pollutants, such as petroleum hydrocarbons in oil spills.

Nitrogen Fixation

The biological transformation of inert atmospheric nitrogen gas ($N_2$) into bioavailable compounds such as ammonia ($NH_3$), performed by specialized diazotrophic bacteria.

Nitrifying Bacteria

Chemoautotrophic soil bacteria that convert ammonia or nitrite ($NO_2^-$) into nitrate ($NO_3^-$), making nitrogen accessible for plant uptake.

Ammonifying Bacteria

Decomposer bacteria that break down nitrogenous organic wastes from dead organisms and convert them into ammonia ($NH_3$) or ammonium.

Binary Fission

The primary asexual reproductive process in bacteria where a single parent cell replicates its circular chromosome, elongates, and constricts at a cleavage furrow to yield two genetically identical daughter cells.

Conjugation

A parasexual transfer of genetic material between two bacteria involving direct contact via a specialized sex pilus, where an $F^+$ donor bacterium replicates and donates plasmid DNA to an $F^-$ recipient.

Transformation

A mechanism of horizontal gene transfer in which a competent bacterial cell absorbs exogenous, naked DNA fragments directly from its extracellular environment.

Transduction

The bacteriophage-mediated transfer of bacterial host DNA fragments from one bacterium to another during viral infection.

Endospore

A highly resilient, dehydrated dormant structure formed within certain bacteria that encloses genetic material in a tough protective coat capable of surviving extreme conditions, including boiling at $100^\circ\text{C}$.

Gram-Positive Bacteria

Bacteria possessing a thick, multilayered peptidoglycan cell wall that retains crystal violet stain to appear purple under a microscope, rendering them more vulnerable to cell-wall targeting antibiotics.

Gram-Negative Bacteria

Bacteria characterized by a thin peptidoglycan layer enclosed by an outer lipopolysaccharide membrane that decolorizes and counterstains pink with safranin.

Chemotaxis

The directed movement of flagellated bacteria toward chemical attractants or away from chemical repellents in their microenvironment.

Obligate Aerobe

An organism that strictly requires molecular oxygen to perform cellular respiration and generate ATP from nutrients.

Obligate Anaerobe

An organism that cannot tolerate molecular oxygen, is actively poisoned by its presence, and relies entirely on anaerobic processes or fermentation (e.g., Clostridium botulinum).

Facultative Anaerobe

An organism capable of generating energy through aerobic respiration when oxygen is available, but able to switch to anaerobic fermentation in its absence without suffering oxygen toxicity.

Aseptic Technique

Standard microbiology laboratory procedures—including flaming inoculating loops until red-hot, tilting culture tubes at a $45^\circ$ angle, and disinfecting surfaces with Lysol and bleach—designed to prevent culture contamination and accidental infection.

Peptidoglycan

A rigid polymer mesh of alternating amino sugars cross-linked by short polypeptide chains that forms the structural backbone of bacterial cell walls.

Nucleoid

The irregularly shaped, non-membrane-bounded region within a prokaryotic cell that contains the primary circular chromosome.

Plasmid

A small, autonomous, extrachromosomal circular DNA molecule found in bacteria that replicates independently of genomic DNA and often carries accessory genes such as antibiotic resistance.

Mesosome

An invaginated fold of the prokaryotic plasma membrane bearing respiratory enzymes essential for ATP synthesis.

Capsule

A dense, organized layer of polysaccharides or proteins surrounding the bacterial cell wall that aids in substrate adherence and protects against host phagocytosis.

Fimbriae

Short, hair-like proteinaceous surface projections that enable prokaryotes to adhere to surfaces, tissues, or one another within a colony.

Thermoacidophile

An extremophilic archaebacterium adapted to survive in habitats characterized simultaneously by high temperatures and high acidity, such as geothermal hot springs and volcanic vents.

Cocci

Spherical or oval-shaped prokaryotic cells that can occur singly, in linear chains (strepto), or in irregular clusters (staphylo).

Bacilli

Rod-shaped prokaryotic organisms.

Spirilli

Rigid or flexible helical- and spiral-shaped prokaryotic organisms.