Microbial Growth and Control Flashcards

Vocabulary practice flashcards covering microbial growth concepts, physical and environmental requirements, culture media, growth measurement methods, and antimicrobial physical and chemical control methods.

Growth

An increase in the number of cells.

Biofilms

An attached polysaccharide matrix containing embedded bacterial cells.

Generation Time

When one cell eventually separates to form two cells, representing the period during which all cellular constituents increase proportionally.

Exponential Growth

A repetitive pattern where the number of cells doubles in a constant time interval, expressed mathematically as a geometric progression of the number 2 ($2^0 \rightarrow 2^1$, $2^1 \rightarrow 2^2$, etc.).

Viable Cell

A cell that is able to divide and form offspring.

Binary Fission

A process where a parent cell divides into two equal daughter cells (common in bacteria and protozoa), forming a totally new daughter cell while the mother cell retains its original identity.

Budding

A process where a new organism grows as a small outgrowth (common in yeast and hydra) where the parent and offspring initially differ in size; the bud remains attached initially before separating into a new organism.

Lag Phase

The phase of growth where growth begins only after a period of time.

Exponential (Log) Phase

The phase where the cell population doubles at regular intervals.

Stationary Phase

The phase where cells in the population grow while others die.

Death Phase

The phase where growth ceases.

Psychrophiles

Cold-loving microbes that grow well at $0^\circ\text{C}$.

Mesophiles

Moderate-temperature-loving microbes that grow best at $25 - 40^\circ\text{C}$ (the most common type of microbe).

Thermophiles

Heat-loving microbes that grow at $50 - 60^\circ\text{C}$.

Hyperthermophiles

Microbes that have an optimum growth temperature of $80^\circ\text{C}$ or higher.

Extreme Thermophiles

Microbes that grow at $121^\circ\text{C}$ and above.

Acidophiles

Bacteria that love acids and grow in acidic environments.

Hypertonic Solution

A solution whose concentration of solutes is higher than in the cell.

Plasmolysis

The shrinkage of cell cytoplasm caused by high osmotic pressures removing necessary water from a cell.

Extreme Halophiles

Halophiles that require high salt concentration for growth.

Obligate Halophiles

Halophiles that require $30\%$ salt for growth.

Facultative Halophiles

Halophiles that require $15\%$ salt for growth.

Obligate Aerobes

Organisms that require oxygen to live.

Facultative Anaerobes

Organisms with the ability to continue growing in the absence of oxygen (e.g., E. coli and yeast).

Obligate Anaerobes

Bacteria that are unable to use molecular oxygen for energy-yielding reactions (e.g., Clostridium).

Aerotolerant Anaerobes

Organisms that cannot use oxygen for growth, but tolerate it fairly well (e.g., Lactobacilli).

Microaerophiles

Aerobic organisms that require oxygen, but grow only in oxygen concentrations lower than those found in air.

Defined Media

Culture media prepared by adding precise amounts of pure inorganic or organic chemicals to distilled water, meaning the exact composition is known.

Complex Media

Culture media made from digests of microbial, animal, or plant products.

Chemostat

The most common type of continuous culture (an open system) used to control both specific growth rate and cell density independently by adding sterile medium at a constant rate while removing an equal volume of spent culture medium at the same rate.

Plate Count

The most frequently used method of measuring bacterial populations, often reported as colony-forming units (CFU).

Serial Dilution

A process where the original inoculum is diluted several times to ensure that resulting colony counts fall within a countable range.

Spread Plate Method

A method where a volume (usually $0.1\,\text{ml}$ or less) of an appropriately diluted culture is spread evenly over the surface of an agar plate using a sterile glass spreader, positioning all colonies on the surface.

Pour Plate Method

A method where a known volume (usually $0.1 - 1.0\,\text{ml}$) of culture is pipetted into a sterile Petri plate and mixed with melted nutrient agar, allowing colonies to grow both within and on the solidified medium.

Most Probable Number (MPN) Method

A statistical estimation method where greater bacterial numbers require more dilutions to reduce density to the point where no bacteria grow in the tubes of a dilution series.

Petroff-Hausser Cell Counter

A counting chamber consisting of a grid with squares of known area etched on the surface of a glass slide, used for direct microscopic counting.

Coulter Counter

An electronic cell counter used for direct measurements.

Sterilization

The removal or destruction (or killing/removal) of all living microorganisms, including viruses and the most resistant forms such as endospores.

Decontamination

The treatment of an object or surface to make it safe to handle, which requires wiping off to remove fragments before using.

Disinfection

A process that directly targets pathogens (using agents called disinfectants) to kill microorganisms or severely inhibit their growth, though it may not eliminate all microorganisms.

Sanitizers

Less harsh agents compared to disinfectants that reduce microbial numbers but do not sterilize.

Antiseptics (or Germicides)

Chemicals that kill or inhibit the growth of microorganisms but are sufficiently nontoxic to animals to be applied to living tissues (commonly used for hand washing or treating surface wounds).

Antimicrobial Agent

A natural or synthetic chemical that kills or inhibits the growth of microorganisms.

-cidal Agents

Antimicrobial agents that actually kill microbes (e.g., bactericidal, fungicidal, viricidal).

-static Agents

Antimicrobial agents that do not kill microbes, but only inhibit their growth (e.g., bacteriostatic, fungistatic, viristatic).

Decimal Reduction Time (D)

The time required for a 10-fold reduction in the viability of a microbial population at a given temperature.

Thermal Death Time

The time it takes to kill all cells at a given temperature.

Autoclave

A sealed heating device that uses steam under pressure ($1.1\,\text{kg/cm}^2$ or $15\,\text{lb/in}^2$) to achieve high temperatures ($121^\circ\text{C}$ for 15 minutes) to kill microorganisms.

Pasteurization

A process using heat to significantly reduce rather than totally eliminate microorganisms found in liquids like milk.

Flash Pasteurization

Heat treatment at $71^\circ\text{C}$ for 15 seconds (or higher temperatures for shorter periods), followed by rapid cooling.

Ultrahigh-Temperature (UHT) Pasteurization

Heat treatment at $135^\circ\text{C}$ for $1 - 2$ seconds that sterilizes milk so it can be stored at room temperature for long periods without spoilage.

Incineration (Burning)

An effective means of destroying contaminated disposable materials using intense heat that ignites and reduces microbes to ashes and gas (limited to metals and heat-resistant glass).

Flaming

An effective way to kill microorganisms by holding the end of a loop or forceps in the yellow portion of a gas flame.

UV Radiation

Electromagnetic radiation with very poor penetrating power, widely used for disinfecting/decontaminating exposed surfaces and air (such as in laboratory laminar flow hoods and hospital/food preparation rooms).

Ionizing Radiation

Electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species from molecules with which the radiation particles collide.

Filtration

A method used to separate cells, larger viruses, bacteria, and certain microbes from liquids or gases in which they are suspended.