Microbiology Comprehensive Review: Viruses, Bacterial Growth, Metabolism, and Infectious Disease

Comprehensive vocabulary flashcards covering the core principles of Virology & Prions, Microbial Growth & Control, Microbial Metabolism & Respiration, and Principles of Infectious Disease & Epidemiology.

Virion

A single, complete, and infectious virus particle that possesses an exterior protective protein capsid and contains internal genetic material ($\text{DNA}$ or $\text{RNA}$).

Capsid

The outer protein shell that encapsulates and protects the viral genome, accounting for the bulk of a virion's mass and formed from repeating protein subunits known as capsomeres.

Helical Capsid

A viral protein shell structured as a hollow, cylindrical tube coiled around the viral nucleic acid.

Icosahedral Capsid

A viral protein shell that takes the form of a three-dimensional polygon, consisting of twenty triangular faces and twelve corners.

Viral Envelope

A host-derived lipid membrane surrounding the capsid of certain animal viruses, acquired when the virus buds outward through a host cell membrane.

Naked Virus

A nonenveloped virus that consists solely of a nucleocapsid without an outer lipid membrane, typically exiting the host cell by cell lysis.

Viral Spikes (Peplomers)

Glycoprotein projections protruding from a viral capsid or envelope that bind to specific surface receptors on host cells to mediate viral attachment and entry.

Antigenic Drift

Spontaneous, minor genetic mutations occurring within viral genome segments that result in subtle alterations in surface antigens (such as influenza HA and NA spikes), enabling the virus to evade host immune detection.

Antigenic Shift

A major genetic reassortment that occurs when two distinct viral strains coinfect the same host cell, combining to produce an entirely new hybrid strain with altered virulence or host range.

Lytic Replication Pathway

A bacteriophage life cycle in which the phage injects its genome, rapidly commandeers host machinery to assemble new virions, and bursts (lyses) the bacterial host cell upon release.

Lysogenic Replication Pathway

A bacteriophage replication process where temperate phage DNA integrates directly into the bacterial host chromosome without immediate lysis, replicating alongside the host cell during division.

Prophage

The latent, integrated viral genome of a temperate bacteriophage embedded within a bacterial host chromosome, which can impart novel virulence factors or toxins to the bacterium via phage conversion.

Specificity

A diagnostic parameter defined as the capacity of a test to recognize and detect only the targeted virus or pathogen without producing false-positive results.

Sensitivity

A diagnostic parameter defined as the capacity of an assay to detect extremely minute quantities of a target pathogen or molecule without producing false-negative results.

Enzyme-Linked Immunosorbent Assay (ELISA)

A surface-bound diagnostic assay that utilizes antigen-antibody binding coupled to an enzymatic reaction to yield a measurable color change indicative of target antigens or antibodies.

Prion

An acellular, infectious misfolded protein lacking nucleic acids ($\text{DNA}$ or $\text{RNA}$) that induces normal cellular proteins in neural tissue to misfold, causing transmissible spongiform encephalopathies (TSEs).

Microbial Growth

Cell division that produces new daughter cells, resulting in an expansion of the total microbial population rather than an increase in the physical dimensions of a single cell.

Biofilm

A structured community of microorganisms adhering to a surface and encased in an extracellular matrix, communicating via chemical signals and exhibiting high resistance to antimicrobials.

Binary Fission

The primary asexual reproductive process in prokaryotes, wherein a single vegetative bacterial cell replicates its circular chromosome and divides into two identical daughter cells.

Generation Time

The time required for a bacterial population to double through binary fission, calculated using the equation: $\text{Generation time} = \frac{\text{Growth time}}{\text{Number of generations}}$.

Lag Phase

The initial interval of a bacterial growth curve in closed culture where cells adjust to their new environment, synthesize required enzymes, and enlarge without increasing overall cell numbers.

Log Phase (Exponential Growth Phase)

The phase of the bacterial growth curve characterized by rapid, exponential cell division at an optimal, constant rate under nutrient-rich conditions.

Stationary Phase

The stage in a bacterial batch culture where cell division and cell death rates become equal due to nutrient depletion and metabolic waste accumulation.

Death Phase

The terminal phase of a closed bacterial culture in which critical accumulation of toxins and extreme nutrient scarcity drive cells to die at an exponential rate.

Psychrophiles

Cold-obligate microorganisms that thrive at temperatures ranging from $-20\,^\circ\text{C}$ to $10\,^\circ\text{C}$.

Psychrotrophs

Cold-tolerant microorganisms capable of growing between $0\,^\circ\text{C}$ and $30\,^\circ\text{C}$, frequently implicated in the spoilage of refrigerated food products.

Mesophiles

Moderate temperature-loving microbes that grow optimally within a range of $10\,^\circ\text{C}$ to $50\,^\circ\text{C}$, encompassing most human pathogens whose optimum is around $37\,^\circ\text{C}$.

Thermophiles

Heat-adapted organisms that grow best at elevated temperatures between $40\,^\circ\text{C}$ and $75\,^\circ\text{C}$, typically residing in hot springs and compost piles.

Extreme Thermophiles

Hyperthermophilic prokaryotes adapted to extreme heat environments between $65\,^\circ\text{C}$ and $120\,^\circ\text{C}$, such as hydrothermal vents.

Halophiles

Microorganisms that thrive in hyper-saline environments, with some obligate species withstanding salt concentrations as high as $35\%$.

Reactive Oxygen Species (ROS)

Chemically reactive, toxic oxygen intermediates (such as superoxide ions and hydrogen peroxide, $\text{H}_2\text{O}_2$) formed during cellular respiration that damage proteins and nucleic acids.

Obligate Aerobe

An organism exhibiting absolute metabolic dependence on molecular oxygen ($\text{O}_2$) and possessing enzymes (such as superoxide dismutase and catalase) to detoxify reactive oxygen species.

Obligate Anaerobe

An organism that does not utilize oxygen in its metabolism and lacks the enzymatic machinery to neutralize reactive oxygen species, resulting in toxicity and cell death in aerobic conditions.

Microaerophile

An organism that requires low amounts of oxygen ($\text{O}_2$) for cellular metabolism and is harmed by atmospheric oxygen concentrations.

Aerotolerant Anaerobe

An anaerobic organism that does not use oxygen ($\text{O}_2$) in its metabolic processes but can tolerate and survive its presence because it possesses enzymes to manage reactive oxygen species.

Facultative Anaerobe

A versatile microbe that prefers using oxygen ($\text{O}_2$) for aerobic cellular respiration, but can switch to fermentation or anaerobic respiration when oxygen is absent.

Sterilization

The complete destruction or elimination of all viable microorganisms, vegetative cells, viruses, and bacterial endospores from an object or environment.

Autoclave

A microbial control apparatus that applies moist heat in the form of steam under pressure to achieve complete sterilization of media, glassware, and surgical instruments.

Pasteurization

A physical control method developed by Louis Pasteur that applies moderate heat (below the boiling point) to eliminate heat-sensitive pathogens and reduce spoilage organisms in liquids.

Catabolism

Exergonic metabolic pathways that break down complex organic molecules into simpler compounds, releasing chemical energy that is harnessed to generate $\text{ATP}$.

Anabolism

Endergonic metabolic pathways that utilize cellular energy (derived from $\text{ATP}$ hydrolysis) and smaller molecular precursors to build complex macromolecules.

Adenosine Triphosphate (ATP)

The principal high-energy currency of the cell, composed of adenine, ribose, and three phosphate groups, used to couple catabolic energy release to anabolic processes.

Enzymes

Biological protein catalysts that accelerate chemical reactions by lowering activation energy without being permanently altered or consumed in the reaction.

Substrate-Level Phosphorylation

A mode of $\text{ATP}$ synthesis wherein an enzyme directly transfers a high-energy phosphate group from an organic metabolic intermediate onto $\text{ADP}$.

Oxidative Phosphorylation

A pathway of $\text{ATP}$ synthesis powered by a series of redox reactions within an electron transport chain, which generates a proton motive force driving $\text{ATP}$ synthase.

Redox Reactions

Coupled chemical reactions where oxidation (loss of electrons) by an electron donor is directly paired with reduction (gain of electrons) by an electron acceptor.

Glycolysis

A universal cytoplasmic pathway that catabolizes one six-carbon glucose molecule into two three-carbon pyruvate molecules, generating a net yield of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Krebs Cycle (Citric Acid Cycle)

A cyclical metabolic pathway that oxidizes two-carbon acetyl groups from acetyl-$\text{CoA}$, producing $\text{CO}_2$, $6\,\text{NADH}$, $2\,\text{FADH}_2$, and $2\,\text{ATP}$ per starting glucose molecule.

Electron Transport Chain

A sequence of membrane-embedded protein complexes and electron carriers that pass electrons via redox reactions, pumping protons to establish a gradient that fuels $\text{ATP}$ synthesis.

Fermentation

An anaerobic catabolic pathway that does not use a respiratory electron transport chain, transferring electrons from $\text{NADH}$ to an organic intermediate (e.g., pyruvate) to regenerate $\text{NAD}^+$ for continued glycolysis.

Exoenzymes

Extracellular enzymes (such as lipases, proteases, and nucleases) secreted by bacteria to digest large, impermeable macromolecules in the external environment into smaller absorbable units.

Catalase Test

A biochemical test identifying organisms that produce the enzyme catalase, detected by the generation of oxygen gas bubbles upon addition of hydrogen peroxide ($\text{H}_2\text{O}_2$).

Oxidase Test

A diagnostic biochemical assay that determines whether a bacterium produces cytochrome c oxidase, indicated by the development of a dark purple/blue color.

Epidemiology

The branch of medicine and public health dedicated to monitoring, evaluating, and controlling disease frequency, distribution, and determinants in human populations.

Opportunistic Pathogen

An agent that causes infectious disease only when the host's immune defenses are weakened, compromised, or when normal resident microbiota are disrupted.

True Pathogen

An infectious microorganism capable of overcoming defenses and causing disease in a healthy, immunocompetent host.

Endemic Infection

An infectious disease that is continuously and routinely detected at a predictable, baseline frequency in a specific geographic area or population.

Epidemic

A sudden, widespread spike in the incidence of a disease in a defined geographic area or population during a specific timeframe, exceeding normal expectations.

Pandemic

An epidemic that expands globally across international boundaries and spreads through multiple continents or worldwide populations.

Zoonotic Disease

An infectious illness that naturally transmits between vertebrate animal reservoirs and humans.

Communicable Disease

An infectious illness capable of being passed directly or indirectly from one human host to another.

Sign

An objective, verified indicator of disease that can be measured or directly observed by an examiner, such as fever, rash, or elevated blood pressure.

Symptom

A subjective physical manifestation of disease that is sensed and reported by the patient but cannot be independently measured, such as pain, nausea, or fatigue.

Koch's Postulates

Four standardized clinical criteria established to verify that a specific microorganism is the causative etiological agent of a particular infectious disease.

Reservoir

The animate or inanimate natural habitat (e.g., animal, human, soil, water) where an infectious pathogen typically lives, replicates, and survives.

Vertical Transmission

A form of direct contact transmission wherein a pathogen is transmitted from an infected mother to her offspring in utero, during vaginal delivery, or post-partum via breast milk.

Biological Vector

An arthropod or animal host (such as a mosquito, tick, or flea) in which a pathogen undergoes part of its life cycle or replication before transmission to another host.

Mechanical Vector

A living vector (such as a housefly or cockroach) that passively transfers pathogens on its body surfaces to hosts or food without supporting pathogen replication or development.

Infectivity

A quantitative measurement that characterizes how effectively an infectious agent can establish an infection within a susceptible host.

Virulence

A measure of the severity of disease or degree of physiological damage inflicted on the host following infection by a pathogen.

Pathogenicity

The general ability of an infectious agent to cause damage or manifest disease in a host organism.

Incubation Period

The asymptomatic phase of infection spanning from initial exposure to a pathogen until the first appearance of clinical signs and symptoms.

Prodromal Phase

The early stage of an infectious disease marked by the onset of mild, generalized, and nonspecific symptoms such as fatigue or malaise as the pathogen begins to multiply.

Acute Phase

The climax or peak stage of an infectious disease where pathogen levels are at their maximum and the host exhibits full-blown, characteristic clinical symptoms.

Convalescent Phase

The final stage of infection during which the pathogen is cleared from the body, symptoms resolve, and the patient recovers to full health.

Epidemiological Triangle

A tripartite model demonstrating the intersection of an etiological agent, a susceptible host, and an environment, which together determine infectious disease occurrence.

Incidence Rate

The frequency metric measuring the number of newly contracted cases of a disease in a specified population over a defined period of time.

Prevalence Rate

The total number of existing cases (both new and pre-existing) of a disease occurring within a defined population at or during a given period.

Herd Immunity

A form of community protection achieved when a sufficiently high proportion (typically around $85\%$) of a population is immune to a pathogen, inhibiting disease spread and protecting unimmunized individuals.