Fundamentals of Microbial Growth, Decontamination, Viruses, and Prions

Comprehensive vocabulary flashcards covering bacterial growth, physical and chemical controls, culturing methods, viral structures, replication, diagnostics, antivirals, and prions.

Microbial growth

Cell division that produces new (daughter) cells and increases the total cell population.

Planktonic bacteria

Free-floating bacterial cells in an environment.

Biofilm

A complex microbial community formed when free-floating (planktonic) bacteria adhere to a surface and undergo sessile growth, communicating and collaborating to survive.

Binary fission

An equal, asexual cell division process occurring in most prokaryotes where a single cell divides to produce two genetically identical daughter cells.

Budding

An asexual reproduction method performed by certain fungi and some bacteria (such as Hyphomicrobium) where the original cell elongates and develops a small outgrowth on one side, resulting in unequal cell division.

Spore formation

A reproductive process performed by some fungi and bacteria; for example, Streptomyces form asexual spores on long hyphae extensions.

Generation time

The time it takes for a cell to divide into two cells (double its population), ranging from $15\text{ minutes}$ to $24\text{ hours}$ depending on species and environmental conditions.

Lag phase

The first phase of bacterial growth in a closed pure batch system, characterized by a delay while cells adjust to their new environment; cells are metabolically active but not dividing rapidly.

Log phase

The second phase of bacterial growth characterized by rapid, exponential cell division via binary fission.

Stationary phase

The third growth phase in a closed system where nutrient depletion and waste accumulation cause the population growth rate to level off, making the number of cells dividing equal to the number of cells dying.

Death phase

The fourth growth phase where waste buildup and nutrient depletion lead to exponential cell death, although a small number of cells may survive by feeding off dead cells (cryptic growth).

Chemostat

An open system continuous culture apparatus in which fresh growth medium is continuously added and waste and excess cells are removed to maintain cells at a specific growth phase.

Minimum temperature

The lowest temperature that supports microbial growth.

Optimal temperature

The temperature at which cellular growth rate and enzymatic activity are highest.

Maximum temperature

The highest temperature that supports microbial growth.

Psychrophiles

Cold-loving microbes that thrive in temperatures ranging from $-20\,^{\circ}\text{C}$ to $10\,^{\circ}\text{C}$.

Psychrotrophs

Cold-tolerant microbes that grow between $0\,^{\circ}\text{C}$ and $30\,^{\circ}\text{C}$, frequently associated with foodborne illness.

Mesophiles

Microbes that grow best between $10\,^{\circ}\text{C}$ and $50\,^{\circ}\text{C}$, representing the classification for most human pathogens.

Thermophiles

Heat-loving microbes that grow around $40\,^{\circ}\text{C}$ to $75\,^{\circ}\text{C}$, commonly found in compost piles and hot springs.

Extreme thermophiles

Microbes that thrive in extreme heat between $65\,^{\circ}\text{C}$ and $120\,^{\circ}\text{C}$, inhabiting environments like boiling water and volcanic vents.

Barophiles

Microbes adapted to withstand high-pressure environments, such as the deep sea.

Acidophiles

Microbes that grow at pH levels from pH $1$ (or less) to pH $5$, maintaining a neutral cytoplasmic pH using proton pumps to export excess protons.

Neutralophiles

Microorganisms that grow best in a pH range of $5$ to $8$, constituting the majority of microbes.

Alkaliphiles

Microbes that grow in basic pH environments ranging from pH $9$ to $11$, maintaining neutral internal cytoplasmic pH via membrane enrichment with acidic compounds.

Halophiles

Microbes that thrive in high-salt environments up to $35\%$ salinity by accumulating organic materials and ions in their cytoplasm to overcome osmotic stress.

Facultative halophiles

Microbes that tolerate elevated salt levels but do not require high salt concentrations to grow (e.g., Staphylococcus aureus).

Reactive oxygen species (ROS)

Toxic, highly reactive oxygen derivatives—such as superoxide ions ($O_2^-$) and hydrogen peroxide ($H_2O_2$)—formed during normal cellular metabolism that can damage proteins and DNA.

Superoxide dismutase

An enzyme that detoxifies reactive superoxide ions ($O_2^-$) by converting them into hydrogen peroxide ($H_2O_2$).

Catalase

An enzyme that detoxifies hydrogen peroxide ($H_2O_2$) by converting it into water ($H_2O$) and oxygen ($O_2$).

Obligate aerobes

Organisms that have an absolute dependence on oxygen for their metabolic processes.

Microaerophiles

Microbes that require small amounts of oxygen for growth and thrive in low-oxygen environments.

Facultative anaerobes

Microbes that can grow in both the presence and absence of oxygen by switching between aerobic cellular respiration and fermentation.

Aerotolerant anaerobes

Microbes that do not use oxygen for metabolic processes (relying strictly on fermentation) but can tolerate oxygen due to mechanisms that deactivate ROS.

Obligate anaerobes

Microbes that do not use oxygen for metabolism and lack enzymes to eliminate ROS, leading to cell death in aerobic environments.

Essential nutrients

Organic and inorganic elements required by microbes to build new cells, categorized into macronutrients (e.g., carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur) and micronutrients (e.g., iron).

Heterotrophs

Organisms that require an external source of organic carbon (such as sugars, lipids, or proteins) because they cannot synthesize their own food.

Autotrophs

Organisms that obtain organic carbon by utilizing carbon fixation to convert inorganic carbon ($CO_2$) into organic compounds.

Growth factors

Necessary organic substances (such as amino acids, vitamins, or nitrogenous bases) that a cell cannot synthesize on its own and must import from its environment.

Fastidious

Term describing organisms that require multiple specific growth factors supplied in their environment or culture medium in order to grow.

Phototrophs

Organisms that utilize light energy to power cellular processes.

Chemotrophs

Organisms that break down chemical compounds to obtain energy.

Broth media

Liquid growth media prepared by adding nutrients to purified water, ideal for growing large batches of microbes in flasks or tubes.

Agar

A powdered polysaccharide extracted from algae used as a solidifying agent in solid and semisolid microbiological growth media.

Defined media

Synthetic culture media in which the precise chemical quantity and identity of every organic and inorganic ingredient is known.

Complex media

Enriched culture media containing complex, non-quantified organic nutrients such as blood, milk proteins (tryptone), or yeast extracts.

Differential media

Culture media formulated to visually distinguish different microbes based on distinct colony appearances or biochemical reactions (e.g., blood agar hemolysis).

Selective media

Culture media containing ingredients that foster the growth of specific desired bacteria while inhibiting the growth of others (e.g., Mannitol salt agar).

Aseptic techniques

Standardized laboratory and clinical procedures designed to prevent introducing contaminating microbes to patients, samples, or culture media.

Streak plate technique

A method of sequentially diluting a bacterial sample across an agar plate using an inoculating loop to yield isolated pure colonies.

Coulter counter

An automated machine that counts cells as they pass through a thin tube, unable to differentiate between living and dead cells.

Flow cytometer

An automated cell-counting system that uses laser light to detect fluorescently tagged cells passing through a narrow channel, enabling differentiation between living and dead cells or cell types.

Viable plate count

A direct cell enumeration method involving serial dilution and spread/pour plating to count living colony-forming units (CFUs) on agar plates, ideally aiming for $30$ to $300\text{ colonies}$.

Turbidity

The cloudiness of a liquid bacterial culture, measured indirectly using a spectrophotometer to evaluate population growth.

Sterilization

The complete destruction or removal of all viable microorganisms, including vegetative bacteria, viruses, and endospores.

Disinfection

The reduction of microbial numbers on inanimate objects or surfaces to render them safe for handling.

Decimal reduction time (DRT)

The time in minutes required to kill $90\%$ of a given microbial population at a specified temperature.

Thermal death time

The shortest period of time required to kill all microbes in a sample at a specific temperature.

Thermal death point

The minimum temperature required to kill all microbes in a liquid sample within $10\text{ minutes}$.

Autoclave

A sterilization apparatus that applies pressurized steam heat ($121\,^{\circ}\text{C}$ at $15\text{ pounds per square inch}$) to sterilize equipment and media, typically within $20\text{ minutes}$.

Pasteurization

The application of moderate heat below a liquid's boiling point to eliminate pathogens and spoilage organisms without sterilizing the liquid.

Ionizing radiation

High-energy radiation (such as gamma rays and X-rays) that generates reactive ions, damages nucleic acids, and sterilizes packaged medical and food products.

Nonionizing radiation

Ultraviolet (UV) light that causes thymine dimers in DNA, used to disinfect surfaces, operating rooms, water, and biosafety cabinets.

HEPA filters

High-efficiency particulate air filters with pore sizes of $0.3\,\mu\text{m}$ or larger that remove $99.97\%$ of airborne particles, microbes, and allergens without sterilizing air.

Germicides

Chemical controls used to limit microbial growth, categorized as microbiocidal (killing microbes) or microbiostatic (inhibiting microbial growth).

Antiseptics

Germicides formulated for safe application on living tissue to reduce or eliminate microbes.

Disinfectants

Germicidal chemicals used to destroy or reduce microbial populations on inanimate objects or surfaces.

Critical equipment

Medical devices that come in contact with sterile body sites or the vascular system (e.g., catheters) and must be completely sterilized.

Semi-critical equipment

Medical instruments that come into contact with mucous membranes or non-intact skin (e.g., endoscopes) and require high-level disinfection.

Non-critical equipment

Healthcare equipment that contacts only intact patient skin (e.g., stethoscopes) and requires low- or intermediate-level disinfection.

Quaternary ammonium compounds (QACs)

Cationic detergents with positive charges that possess bactericidal and sporostatic activities.

Virology

The scientific study of viruses.

Virus

A submicroscopic, acellular, nonliving infectious agent that is an obligate intracellular pathogen consisting of a protein capsid and a DNA or RNA genome.

Bacteriophages

Viruses that specifically infect bacterial cells.

Virion

A single, complete, infectious virus particle outside a host cell.

Capsid

The protein shell that encapsulates and protects the viral genome, made of individual capsomere protein subunits.

Enveloped viruses

Viruses surrounded by an outer lipid-based layer acquired by budding off from the host cell's plasma membrane.

Naked viruses

Nonenveloped viruses that lack a lipid membrane and arise from host cells via cellular lysis.

Spikes (Peplomers)

Glycoprotein extensions projecting from a viral capsid or envelope that bind specifically to surface factors on host cells to mediate viral attachment and entry.

RNA-dependent RNA polymerases (RdRPs)

Viral enzymes that transcribe single-stranded negative-sense RNA (ssRNA-) viral genomes into complementary mRNA for translation by host ribosomes.

Reverse transcriptase

An enzyme used by retroviruses to convert their single-stranded RNA genome into a double-stranded DNA intermediate.

Attenuated strains

Weakened viral variants produced by genetic mutations that limit disease-causing ability in a healthy host while retaining the capacity to stimulate an immune response.

Tropism

The specific preference of a virus for infecting particular host cell types, tissues, or organs.

Host range

The range or collection of species that a specific virus can infect.

Antigenic drift

Minor, gradual changes in viral surface antigens (e.g., HA and NA spikes) caused by spontaneous point mutations during genome replication.

Antigenic shift

A major genetic reassortment that occurs when two different viral strains co-infect the same host cell, resulting in novel spike protein combinations that can cause pandemics.

Lytic replication pathway

A bacteriophage replication pathway involving attachment, penetration, replication, assembly, and host cell lysis to release new virions.

Temperate phages

Bacteriophages capable of reproducing through either lytic or lysogenic replication pathways.

Lysogenic replication

A viral replication strategy where the phage genome integrates into the host bacterial chromosome, forming a prophage that replicates along with the host cell.

Prophage

The integrated form of a bacteriophage genome within a host bacterial chromosome during lysogenic replication.

Phage conversion

The acquisition of new genetic and pathogenic traits (such as toxin production) by a host bacterium due to expression of prophage genes.

Uncoating

The animal virus replication step during which the protein capsid is enzymatically degraded to release the viral genome into the host cell cytoplasm or nucleus.

Acute infections

Nonpersistent viral infections in which new virions are produced immediately and the infection resolves rapidly or leads to host cell death.

Persistent infections

Long-term viral infections in which the virus evades host immune clearance through continuous release or latent reactivation strategies.

Chronic persistent infections

Persistent viral infections characterized by continuous, low-level release of virions over months or years with slow disease progression.

Provirus

The integrated viral DNA formed when an animal virus (e.g., HIV) inserts its genetic material into the host cell genome.

Latent persistent infections

Persistent viral infections characterized by intermittent periods of dormancy (latency) interrupted by symptomatic flare-ups and active viral shedding.

Oncogenic viruses

Viruses capable of inducing cancer in host cells by stimulating uncontrolled cell division or inhibiting normal cell death signals.

Plaque assay

A laboratory method used to enumerate infectious bacteriophages by counting clear zones (plaques) on a bacterial lawn, expressed as plaque-forming units (PFU/mL).

Latex agglutination test

A diagnostic assay in which viral antigens or specific antibodies attached to latex beads form visible clumps upon binding their targets.

ELISA (Enzyme-Linked Immunosorbent Assay)

A diagnostic assay that uses antigen-antibody binding linked to enzyme-mediated color changes to detect viral antigens or antibodies in liquid samples.