Microbiology: Viral Biology, Bacterial Genetics, Microbial Growth, and Control Methods

Comprehensive vocabulary flashcards covering key terms and concepts across viral structure, bacterial genetics, microbial growth parameters, and physical and chemical control methods.

Capsid

The protein coat that encloses and protects the viral nucleic acid genome and serves to transport it to host cells.

Capsomeres

The individual protein subunits that assemble to form the outer viral capsid.

Nucleocapsid

The combined viral structure consisting of the capsid together with its enclosed nucleic acid genome.

Viral Envelope

A lipid bilayer acquired from the host cell phospholipid membrane when the virus exits, offering extra protection and aiding cellular entry.

Non-Enveloped (Naked) Viruses

Viruses lacking a surrounding lipid bilayer that enter host cells via endocytosis; they are more resistant to disinfectants and more readily recognized by the immune system.

Spikes

Viral protein surface projections that attach to specific receptor sites on host cells.

Host Range

The specific spectrum of species and host cell types that a given virus is capable of infecting, dictated by host cell surface receptors.

Zoonoses

Infectious diseases that can be transmitted from animal reservoirs to human hosts either directly, indirectly, or via an intermediate vector.

Vector

An intermediate organism, such as a tick or arthropod, that carries and transmits zoonotic pathogens from animal reservoirs to humans.

Temperate Phage

A bacteriophage that can integrate its DNA into the host bacterial chromosome without causing immediate lysis, producing progeny when induced.

Virulent Phage

A bacteriophage that undergoes a lytic cycle to replicate and lyse the host bacterium, leading directly to host cell death.

Lysogen

A bacterium that carries a prophage integrated into its chromosomal DNA.

Lysogenic Conversion

A change in the phenotype or physiological properties of a bacterial cell resulting from the integration of a phage genome.

Prophage

The latent form of a bacteriophage whose genome is integrated into the host bacterium's chromosome.

Subacute Sclerosing Panencephalitis (SSPE)

A rare but fatal central nervous system complication of measles that manifests $7\text{--}10\,\text{years}$ after initial infection.

Genotype

The precise sequence of nucleotides and genetic content of an organism, representing its inherited blueprint.

Phenotype

The observable physical, biochemical, or physiological properties of an organism resulting from the expression of its genotype and influenced by the environment.

Vertical Gene Transfer

The transfer of genetic information and mutations from a parent organism to its offspring across generations.

Horizontal Gene Transfer

The acquisition and sharing of genetic material between independent bacterial cells within the same generation.

Plasmid

A small, circular, extrachromosomal double-stranded DNA molecule that replicates independently and often carries genes conferring antibiotic resistance or virulence.

R Plasmid

A circular double-stranded DNA resistance plasmid that carries genes conferring resistance to antimicrobial agents.

Transformation

A mechanism of horizontal gene transfer in which a competent bacterial cell takes up naked, free DNA directly from the external environment.

Transduction

A mechanism of horizontal gene transfer in which a bacteriophage mistakenly packages bacterial DNA and delivers it to a recipient bacterium.

Conjugation

A mechanism of bacterial horizontal gene transfer involving direct cell-to-cell contact through a conjugation pilus and cytoplasmic bridge.

Pathogenicity Islands

Large segments of bacterial DNA containing multiple genes encoding toxins and virulence factors, frequently associated with prophages.

Plasmid pXO1

A virulence plasmid found in Bacillus anthracis that encodes a three-part exotoxin consisting of protective antigen, edema factor, and lethal factor.

Plasmid pXO2

A virulence plasmid found in Bacillus anthracis that encodes an antiphagocytic capsular polysaccharide enabling immune evasion.

Missense Mutation

A base substitution mutation in a gene that alters a codon so that a different amino acid is incorporated into the synthesized protein.

Nonsense Mutation

A base substitution mutation that converts an amino acid codon into a premature stop codon, producing a truncated protein.

Ames Assay

A bacterial screening procedure utilizing a histidine-auxotrophic strain of Salmonella typhimurium to determine whether a chemical compound has mutagenic and potential carcinogenic activity.

Pure Culture

A laboratory population of microorganisms derived from a single progenitor cell and containing only one distinct species.

Colony

A visible macroscopic mass of microorganisms growing on a solid nutrient agar medium, derived from the multiplication of a single isolated cell.

Binary Fission

The primary mode of asexual reproduction in prokaryotes by which a single bacterial cell divides into two identical daughter cells.

Log Phase (Exponential Growth)

The phase of the bacterial growth curve characterized by rapid, constant cell division and maximal metabolic rate under ideal conditions.

Stationary Phase

The bacterial growth curve phase where the cell multiplication rate equals the cell death rate as nutrients deplete and metabolic waste accumulates.

Hemocytometer

A calibrated, specialized glass slide with a grid pattern used for manual direct microscopic cell counting of larger cells such as yeast and mammalian cells.

Coulter Counter

An automated instrument that electronically counts individual cells in a conducting liquid as they pass through a narrow aperture detector.

Turbidity

The cloudiness of a microbial broth culture measured by spectrophotometer absorbance, serving as an indirect indicator of microbial biomass.

Obligate Aerobes

Microorganisms that have an absolute metabolic requirement for molecular oxygen to grow and survive.

Obligate Anaerobes

Microorganisms that cannot grow in the presence of molecular oxygen and are typically harmed or killed by oxygen exposure.

Facultative Anaerobes

Microorganisms capable of metabolic growth and division under either aerobic or anaerobic environmental conditions.

Microaerophiles

Microorganisms that require reduced concentrations of molecular oxygen ($2\text{--}10\%$) for optimal growth.

Aerotolerant Anaerobes

Microorganisms that do not use oxygen for metabolic energy generation but are indifferent to and can tolerate its presence.

Catalase Test

A biochemical test detecting the enzyme catalase by adding hydrogen peroxide to microbes, where positive results show visible bubbling from oxygen gas release.

Psychrophile

A cold-adapted microorganism that exhibits an optimal growth temperature between $-5^\circ\text{C}$ and $15^\circ\text{C}$.

Psychrotroph

A microorganism with an optimum growth temperature between $20^\circ\text{C}$ and $30^\circ\text{C}$ that is capable of growing well at refrigeration temperatures.

Mesophile

A microorganism that grows optimally at temperatures between $25^\circ\text{C}$ and $45^\circ\text{C}$, including normal human body temperature ($37^\circ\text{C}$).

Thermophile

A heat-tolerant microorganism with an optimum growth temperature between $45^\circ\text{C}$ and $70^\circ\text{C}$.

Hyperthermophile

An extremophilic microorganism that grows optimally at temperatures of $70^\circ\text{C}$ or greater.

Halotolerant

Microorganisms that can withstand and grow in environments with high salt concentrations up to approximately $10\%$, such as Staphylococcus aureus.

Halophile

Microorganisms that strictly require high ambient salt concentrations ($3\%$ to $9\%$) in their growth medium.

Selective Media

Culture media formulated with ingredients that inhibit the proliferation of unwanted organisms while supporting the growth of target microbes.

Differential Media

Culture media containing biochemical indicators that allow different species to be distinguished visually based on their metabolic characteristics.

Fomite

An inanimate object that can harbor and transmit infectious microorganisms between human hosts.

Sterilization

The complete destruction or physical elimination of all viable microbial life forms, including bacterial endospores and viruses (excluding prions).

Aseptic Technique

Specific laboratory and clinical protocols implemented to maintain sterility and prevent microbial contamination of equipment, cultures, and patients.

Commercial Sterilization

Industrial thermal processing used in food canning to destroy heat-resistant endospores of dangerous pathogens like Clostridium botulinum.

Disinfection

The destruction or elimination of most vegetative pathogens on inanimate surfaces or objects.

Pasteurization

A brief heat treatment that significantly reduces numbers of heat-sensitive pathogens and spoilage organisms in liquids without achieving complete sterilization.

Antiseptics

Antimicrobial chemical agents formulated for safe topical application to living skin and tissues to inhibit or destroy microbes.

Degerming

The mechanical removal or reduction of the microbial load on a localized area of living tissue, such as skin preparation prior to an injection.

Sanitation

The reduction of microbial numbers on surfaces or materials to safe levels established by public health regulations.

Autoclave

A device utilizing pressurized steam at $121^\circ\text{C}$ and $15\,\text{psi}$ for at least $15\,\text{minutes}$ to achieve complete sterilization, destroying endospores.

High-Temperature Short-Time (HTST) Pasteurization

A pasteurization method that heats liquid foods like milk to $72^\circ\text{C}$ for $15\,\text{seconds}$ to kill pathogens while preserving flavor and quality.

Ultra-High Temperature (UHT) Pasteurization

A thermal processing method that subjects liquid foods to $138^\circ\text{C}$ for $2\,\text{seconds}$ or more, enabling sterile unrefrigerated shelf storage.

Ethylene Oxide

A gaseous chemical sterilant used to sterilize heat- and moisture-sensitive materials such as fabrics, pacemakers, artificial hips, and petri dishes.

Silvadene Cream

A topical silver-containing antimicrobial formulation used as an antiseptic to prevent and treat infections in burn wounds.

Silver Nitrate Drops

A topical silver-based antiseptic applied to the eyes of neonates to prevent ophthalmia neonatorum.

Disk Diffusion Assay

A laboratory method used to evaluate germicide effectiveness by placing chemical-impregnated paper disks on an inoculated agar plate and observing the clear zone of inhibition.