Microbial Growth, Environmental Pressures, Controls, and Metabolism

Comprehensive vocabulary flashcards covering microbial environmental limits (pH, temperature, salinity, oxygen), physical and chemical control methods, antibiotic targets and resistance mechanisms, and fundamental microbial metabolism.

Osmosis

The diffusion of water from regions of high water concentration to lower water concentration, or from lower solute concentration to higher solute concentration.

Neutrophile

An organism that grows optimally in environments with a pH greater than 5.5 and less than 8.

Acidophile

An organism that grows optimally at a pH less than or equal to 5.5.

Alkaliphile

An organism that grows optimally at a pH greater than or equal to 8.

Picrophilus oshimae

An acidophilic species of Archaea found in acidic thermal volcano soils that grows optimally at pH 0.7 and spontaneously lyses at pH > 4.

Sodium Motive Force

A bioenergetic mechanism used by certain alkaliphiles, such as Bacillus firmus, relying on $Na^+$ instead of $H^+$ to drive transport reactions and rotate flagella.

Halophile

An organism that requires high concentrations of salt (NaCl) for growth.

Halotolerant

An organism that tolerates elevated levels of salt but grows best in its absence.

Osmophile

An organism that lives in environments high in sugar content.

Xerophile

An organism capable of living in extremely dry environments characterized by a lack of water.

Aerobe

An organism that grows in the presence of atmospheric oxygen and respires $O_2$ in its metabolism.

Microaerophile

An organism that requires oxygen for growth but at reduced levels compared to atmospheric air (< 21% $O_2$).

Facultative Aerobe

An organism that does not strictly require oxygen for growth, but grows better in its presence.

Aerotolerant Anaerobe

An organism that cannot respire oxygen, but can tolerate and grow in its presence.

Anaerobe

An organism that cannot respire oxygen.

Thioglycolate

A reducing agent added to media to eliminate oxygen by reducing it to water.

Catalase

An enzyme that detoxifies hydrogen peroxide by converting it into water and oxygen ($H_2O_2 + H_2O_2 \rightarrow 2\,H_2O + O_2$).

Decontamination

The treatment of an object or surface to render it safe to handle.

Disinfection

A treatment process directly targeting pathogens, although it may not eliminate all microorganisms.

Heat Sterilization

The use of elevated heat, such as in autoclaves at $121^{\circ}\text{C}$ for ~15 min, to kill all microorganisms, including bacterial endospores.

Pasteurization

A heat treatment process designed to significantly reduce the microbial load in liquids (e.g., heating milk to $71^{\circ}\text{C}$ for $15\,\text{sec}$) without achieving complete sterilization.

Ultraviolet Radiation (UV)

Electromagnetic radiation between $220\,\text{nm}$ and $300\,\text{nm}$ that induces DNA mutations causing cell death; limited by poor penetration power.

Ionizing Radiation

Electromagnetic radiation (such as X-rays) that produces ions and reactive molecular species, with sufficient penetrating power to sterilize bulk items and medical supplies.

Depth Filter

A filter composed of a fibrous sheet of overlapping paper or glass fibers that traps particles within a dense network, used in HEPA filters.

Conventional Membrane Filter

A filter made of high-tensile-strength polymers containing microscopic pores (typically $\ge 0.2\,\mu\text{m}$) used to sterilize heat-sensitive liquids.

Nucleopore Filter

A thin polycarbonate film treated with radiation and etched chemically to create uniform holes, used to isolate organisms for scanning electron microscopy (SEM).

Bacteriostatic Agent

An antimicrobial agent that inhibits bacterial growth without killing the cells.

Bactericidal Agent

An antimicrobial agent that kills bacterial cells without causing cell lysis.

Bacteriolytic Agent

An antimicrobial agent that kills bacterial cells by causing cell lysis.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial agent required to completely inhibit the visible growth of a microorganism.

Diffusion Disk Assay

A laboratory method used to assess microbial susceptibility by measuring zones of growth inhibition around drug-infused disks on a agar plate inoculated with a test organism.

Extremophile

An organism adapted to grow in conditions that are ecologically extreme, such as very high/low temperatures or extreme pH.

Cardinal Temperatures

The minimum, optimum, and maximum temperatures that define the environmental temperature limits for the growth of a specific organism.

Psychrophile

A microorganism with an optimal growth temperature below $15^{\circ}\text{C}$, a maximum growth temperature below $20^{\circ}\text{C}$, and a minimum growth temperature below $0^{\circ}\text{C}$.

Psychrotolerant

Microorganisms that are capable of growing at $0^{\circ}\text{C}$ but have optimal growth temperatures between $20^{\circ}\text{C}$ and $40^{\circ}\text{C}$.

Cold Shock Proteins

Proteins synthesized under cold stress that bind to RNA and DNA molecules, stabilizing them to maintain functional transcription and translation.

Cryoprotectant

Antifreeze proteins or chemical solutes (such as glycerol) that prevent ice crystal formation and protect cytoplasmic membranes from rupture during freezing.

Thermophile

An organism with a growth temperature optimum above $45^{\circ}\text{C}$.

Hyperthermophile

An organism with a growth temperature optimum above $80^{\circ}\text{C}$.

Taq Polymerase

A heat-stable DNA polymerase isolated from Thermus aquaticus used in automated polymerase chain reaction (PCR) amplification.

Metabolism

The complete collection of chemical reactions occurring within a living organism to maintain life.

Respiration

An aerobic or anaerobic catabolic process where an organic or inorganic electron donor is oxidized to release usable energy.

Anabolism

The energy-requiring (endergonic) pathway of metabolism involved in synthesizing complex molecules from simpler ones.

Catabolism

The energy-releasing (exergonic) pathway of metabolism involving the breakdown of complex molecules into simpler compounds.

Autotroph

An organism that utilizes inorganic carbon ($CO_2$) as its primary carbon source.

Heterotroph

An organism that derives its carbon from organic compounds produced by other living organisms.

Phototroph

An organism that utilizes light as its principal energy source.

Chemotroph

An organism that obtains its energy from the oxidation of organic or inorganic chemical compounds.

Chemolithotroph

An organism that obtains energy from the oxidation of inorganic carbon/chemical compounds.

Chemoorganotroph

An organism that obtains energy from the oxidation of organic carbon compounds.

Activation Energy

The minimum energy required to break chemical bonds and initiate a reaction, which enzymes lower to accelerate reaction rates.

Glycolysis

A catabolic pathway that breaks down glucose into pyruvate, yielding energy in the form of ATP.

Citric Acid Cycle

A cyclic metabolic pathway that oxidizes acetyl-CoA into 4C and 6C intermediates, generating ATP, electron carriers (NADH and $FADH_2$), and $CO_2$.

Efflux Pump

A membrane protein system (such as AcrAB-TolC) that actively pumps antimicrobial molecules out of the bacterial cell, conferring antibiotic resistance.

\beta-Lactamase

An enzyme produced by resistant bacteria that inactivates \beta-lactam antibiotics like penicillin by cleaving their chemical structure.