Microbiology Chapter 6: Microbial Growth Flashcards

Vocabulary flashcards covering the physical and chemical requirements for microbial growth, types of culture media, growth phases, and measurement techniques from Chapter 6.

Psychrophiles

Cold-loving microbes that live in deep oceans and polar regions.

Mesophiles

Moderate-temperature-loving microbes, which include normal microbiota and pathogens of animals.

Thermophiles

Heat-loving microbes with an optimum growth temperature of $50$ to $60^\circ C$, often found in hot springs and organic compost piles.

Psychrotrophs

Microbes capable of growth at $0^\circ C$ with an optimum between $20$ and $30^\circ C$; these are the primary cause of food spoilage in refrigerators.

Hyperthermophiles

Also known as extreme thermophiles, these organisms have an optimum growth temperature of $80^\circ C$ or higher.

Acidophiles

Organisms that specifically grow in acidic environments.

Plasmolysis

Shrinkage of the cell’s cytoplasm caused by the movement of water out of the cell in hypertonic environments.

Extreme halophiles

Also known as obligate halophiles, these require high salt concentrations for growth, as high as $30\%$ NaCl.

Facultative halophiles

Organisms that do not require high salt but tolerate concentrations between $2\text{--}10\%$ NaCl.

Chemoheterotrophs

Organisms that use organic molecules as both their carbon source and energy source.

Autotrophs

Organisms that use $CO_2$ as their primary carbon source.

Nitrogen fixation

The process by which a few bacteria use gaseous nitrogen ($N_2$) directly from the atmosphere.

Trace elements

Inorganic elements like iron, copper, molybdenum, and zinc required in small amounts, typically used as enzyme cofactors.

Obligate aerobes

Microbes that require oxygen to live.

Facultative anaerobes

Microbes capable of growing with or without oxygen; they use fermentation or anaerobic respiration when oxygen is absent.

Aerotolerant anaerobes

Microbes that cannot use oxygen for growth but can tolerate its presence.

Microaerophiles

Microbes that require oxygen for growth but only in concentrations lower than those found in the air.

Superoxide dismutase (SOD)

An enzyme produced by cells that use or tolerate oxygen to remove highly reactive superoxide radicals ($O_2^-$).

Biofilms

Microbial communities that form slime or hydrogels, communicate via quorum sensing, and are involved in $70\%$ of human infections.

Inoculum

The process or substance used for the introduction of microbes into a culture medium.

Agar

A complex polysaccharide from algae used as a solidifying agent that liquefies at $100^\circ C$ and solidifies at approximately $40^\circ C$.

Chemically defined media

A culture medium where the exact chemical composition is known.

Fastidious organisms

Organisms that require many specific organic growth factors provided within their media.

Complex media

Media made of extracts and digests from yeasts, meat, or plants where the exact chemical composition varies from batch to batch.

Reducing media

Special media used for anaerobic bacteria cultivation containing chemicals like sodium thioglycolate that deplete dissolved oxygen.

Capnophiles

Microbes that require higher concentrations of $CO_2$ than what is found in the atmosphere.

Selective media

Media designed to suppress the growth of unwanted microbes and encourage the growth of desired microbes.

Differential media

Media that make it easier to distinguish colonies of different microbes on the same plate.

Enrichment culture

Usually a liquid medium providing nutrients that favor the growth of a particular microbe to detectable levels from a small initial population.

BSL-4

Biosafety Level 4, reserved for the most dangerous 'hot zone' pathogens, requiring sealed, negative pressure labs and HEPA-filtered exhaust.

Colony-forming unit (CFU)

A visible population of cells arising from a single cell, spore, or group of attached cells.

Lyophilization

A preservation method also known as freeze-drying where bacteria are frozen and then dehydrated in a vacuum.

Binary fission

The primary method of bacterial division where a single cell replicates its chromosome and divides into two identical cells.

Generation time

The time required for a bacterial cell to divide or for a population to double, ranging from $20 \text{ minutes}$ up to $24 \text{ hours}$.

Lag phase

The initial period of the bacterial growth curve characterized by little or no cell division but intense metabolic activity.

Log phase

Also called the exponential growth phase, it is the period of most rapid cellular reproduction where generation time is at a minimum.

Stationary phase

The growth phase where the number of new cells produced equals the number of cell deaths, often due to reaching carrying capacity.

Death phase

The phase where the number of cell deaths exceeds the formation of new cells, leading to a logarithmic decline in population.

Serial dilution

A process used to dilute an original inoculum to ensure that plate counts result in a manageable $30$ to $300$ colonies.