BIOL 2730 Chapter 4: Microbial Growth & Control Flashcards

91 question-and-answer study flashcards covering Chapter 4: Microbial Growth & Control from BIOL 2730.

What is binary fission?

The asexual process of reproduction in which one cell divides into two daughter cells.

What is generation time?

The time it takes for a population to double in number.

What factors influence generation time?

It varies greatly from species to species and is influenced by the conditions in which the cells are grown.

What does microbial growth refer to?

Growth of populations rather than an increase in individual cell size.

What is a biofilm?

A microbial community that grows attached to a surface; the lecture gives examples such as tooth scuz, lake rocks, catheter surfaces, house pipes, plastic tubing, and shower floors.

What surface is described as most resistant to biofilm formation?

Copper.

What are the macronutrients listed in the lecture?

Carbon, nitrogen, sulfur, phosphorus, potassium, magnesium, calcium, and iron.

What are micronutrients?

Trace elements such as cobalt, zinc, copper, molybdenum, and manganese, among others.

What are macronutrients used for?

They are used to create the physical and chemical structures of the cell.

What are micronutrients typically used for?

They are typically enzymatic cofactors and can vary from organism to organism.

What happens when the supply of macro- or micronutrients is insufficient?

An insufficient supply of either can limit microbial growth.

What else do microorganisms require besides nutrients?

High-energy molecules that they can metabolize as food.

What are the three energy sources listed in the lecture?

Sunlight, organic matter, and inorganic matter.

What is phototrophy?

Obtaining energy from sunlight.

What is chemoorganotrophy?

Obtaining energy from organic matter.

What is chemolithotrophy?

Obtaining energy from inorganic matter.

What are growth factors?

Specific nutritional factors, such as vitamins, that some bacteria require for growth.

What does fastidious mean when describing bacteria?

Having complicated growth requirements.

What is a complex medium?

A growth medium containing a variety of ingredients, such as meat juices and digested proteins, sometimes with additional mixed nutrients.

What is a chemically defined medium?

A medium composed of exact amounts of pure chemicals.

What is a selective medium?

A medium that inhibits the growth of certain species, making it easier to isolate the organism being sought.

What is a differential medium?

A medium that tests for a biochemical capability and contains chemicals that certain microbes change in a recognizable way, usually by changing color.

What is blood agar differential for?

Hemolysis.

What is beta hemolysis?

A zone of complete clearing around a colony growing on $5\%$ blood agar.

What is alpha hemolysis?

A zone of greenish clearing around a colony on blood agar.

What is gamma hemolysis?

No hemolytic reaction.

What is a pure culture?

A culture containing only a single kind of microbe.

What is a contaminant?

An unwanted organism in a culture.

In what forms can cells be grown in culture media?

Liquid or solid culture media.

How are solid media prepared?

By adding a gelling agent such as agar or gelatin.

What do cells form when grown on solid media?

Isolated masses called colonies.

Why is sterilization of media critical?

Because microbes are everywhere, so unwanted organisms must be eliminated before culturing the organism of interest.

What is aseptic technique?

The set of practices used to prevent unwanted microbial contamination during culture and transfer.

What is confluent growth?

Growth in which colonies are so close together that they merge into essentially continuous growth.

What are isolated colonies?

Separate colonies that can be distinguished from one another, commonly seen toward the end of a streak.

What are the five stages of the batch-culture growth curve?

Lag phase, exponential/log phase, stationary phase, death phase, and phase of prolonged decline.

What is a batch culture?

A closed-system culture in which no additional nutrients are added and wastes are not removed.

During which phase is generation time measured?

The log (exponential) phase.

What happens during the lag phase?

The cells are adapting to the new environment before rapid population growth.

What happens during the exponential/log phase?

Cells multiply rapidly at their maximum growth rate under the provided conditions.

What happens during the stationary phase?

Population growth levels off as conditions such as nutrients and waste accumulation limit further net growth.

What happens during the death phase?

Viable cells decrease as unfavorable conditions continue.

What is the phase of prolonged decline?

The later stage of the growth curve in which the viable population continues to decline over an extended period.

What is a continuous culture?

An open-system culture in which growth medium is added and removed after the system is established.

Why is continuous culture used?

To keep the culture in log phase or to collect waste products from the medium.

What is a chemostat?

A device used for continuous culture in which growth conditions can be maintained by controlled addition/removal of medium.

Why do bacterial cultures grow quickly under favorable conditions?

Bacterial growth is logarithmic, so cultures rapidly approach their maximum growth rate under the provided conditions.

What are primary metabolites?

Metabolites synthesized during active multiplication.

Give examples of primary metabolites listed in the lecture.

Ethanol and commercial amino acids for supplements.

When are secondary metabolites synthesized?

They begin to be synthesized in late log phase.

What are common examples of secondary metabolites?

Most antibiotics.

What is an enrichment culture?

A culture used when a sample is dilute or an organism of interest is uncommon; growth factors are added that allow the desired organism to grow faster than most others.

What is the goal of enrichment?

To increase the number of the organism of interest to levels where it can be readily detected or cultured.

What is one common application of enrichment culture mentioned in the lecture?

Water testing.

What is a direct microscopic count?

A method of estimating or determining cell numbers by directly examining and counting cells microscopically.

What is a hemocytometer used for?

Direct microscopic counting using a chamber with a known volume.

How does a hemocytometer work?

A culture is loaded into a counting chamber of known volume, cells are counted in sections of the grid, and the count is multiplied using the provided formula to enumerate cells.

What is a Coulter counter used for?

It optically counts cells as they pass through a narrow channel and provides an accurate concentration.

How does a spectrophotometer estimate cell number?

It uses turbidity/optical density to estimate cell concentration.

What must be done before turbidity can reliably estimate cell concentration?

A one-time test must establish the correlation between optical density and cell concentration for the specific organism and conditions.

What are spread plates and pour plates used for?

Viable cell counts using small amounts of liquid culture inoculated onto appropriate growth media.

What does a viable cell count measure?

The number of living, culturable cells capable of producing colonies under the conditions used.

Why are serial dilutions used?

To decrease the concentration of cells in a sample so individual colonies can be counted.

What dilution is commonly used in serial dilution according to the lecture?

Ten-fold (10-fold) dilutions.

What sample can be used for serial dilution?

Cells can be serially diluted in media or sterile water before plating.

What colony-count range is considered statistically valid for a plate?

30–300 colonies per plate.

What is membrane filtration used for?

It concentrates microbial cells before they are plated.

What are cardinal temperatures?

The minimum, optimum, and maximum temperatures at which a microorganism can grow.

Why does temperature dramatically affect bacterial growth?

Because temperature affects cellular enzymes.

What does a microorganism's optimum temperature usually reflect?

Its common habitat.

Into how many groups are prokaryotes commonly divided based on optimum growth temperature?

Five groups.

Where is the optimum temperature usually located within a microorganism's growth range?

Near the upper limit of its growth range.

What should you remember about psychrophiles from the lecture?

They grow at temperatures below body temperature.

What should you remember about thermophiles from the lecture?

They grow at temperatures much higher than body temperature.

What is pH?

The negative logarithm of the hydrogen ion concentration of a solution.

What pH range do most microbes (neutrophiles) live and multiply within according to the lecture?

Approximately pH 5 to pH 8.

What is the optimum pH for most microbes?

Near neutral, around pH 7.

What are neutrophiles?

Microorganisms that grow best near neutral pH and commonly live/multiply within about pH 5–8.

What are acidophiles?

Microorganisms that grow optimally at a pH below 5.5.

What are alkaliphiles?

Microorganisms that grow optimally at a pH above 8.5.

How does solute concentration affect a microbial cell?

Because the cytoplasmic membrane allows water to pass freely, a higher solute concentration outside the cell causes water to move out of the cell.

What is the most medically relevant solute mentioned in the lecture?

Salt.

What other common solute is mentioned?

Sugar.

What are halotolerant bacteria?

Bacteria that can tolerate high salt concentrations, up to about $10\%$ $NaCl$ according to the lecture.

What are halophiles?

Organisms that require high-salt conditions.

Do organisms that do not use oxygen for metabolism still have enzymes that interact with oxygen-derived compounds?

Yes. The lecture states that all organisms have enzymes that can split $O_2$ into oxygen radicals.

What primarily determines tolerance to oxygen?

The presence of specific enzymes, such as catalase, that help eliminate activated oxygen species.

What are examples of activated oxygen species mentioned?

Superoxide and peroxide.

What does catalase help do?

It helps eliminate activated oxygen species.

What is an anaerobic growth container used for?

To create an anaerobic environment by removing oxygen.

How does the disposable anaerobic packet work?

Chemicals in the packet react with $O_2$, producing an anaerobic environment.