🧫Chapter 4: Microbial Growth

True or False: Some species of microorganisms can be found in environments where no unprotected human could survive.

True

How do bacterial cells divide?

By the process of binary fission.

What are the stages of binary fission?

1. Cell gets longer and DNA replicates; 2. DNA moves to each future daughter cell and cross wall forms; 3. Cell divides into two daughter cells; 4. Daughter cells separate.

How many cells can ten cells of a pathogen give rise to in a matter of hours due to exponential multiplication?

Over 40,000 cells.

What is the generation time of E. coli?

About 20 minutes.

If 1 million E. coli cells are intubated, how many would be present after 1 hour?

8 million.

What is the least likely explanation for not successfully isolating prokaryotes?

Conditions in mixed microbial associations are readily reproduced in the lab.

Which environment is more changing and complex?

Soil and its surroundings.

Which structure is most closely associated with biofilm formation?

Slime layers.

What is one benefit of existing in a biofilm for microbes?

Helps microbes stay in microenvironments in which they thrive.

Which of the following does NOT describe interactions of mixed microbial communities?

Conditions in mixed microbial associations are readily reproduced in the lab.

What is a pure culture?

A culture that contains only one type of organism.

Approximately what percentage of all prokaryotes can currently be grown in culture successfully?

1%.

What are two examples of harmful biofilms?

Dental plaque in people and corrosive biofilms in pipelines.

What characterizes a sterile medium?

A complete absence of viable microbes.

What is a bacterial colony?

A distinct mass of cells on a solid medium.

What is the order of exponential growth stages?

1. Lag; 2. Exponential; 3. Stationary; 4. Death.

Which two methods are best for long-term storage of microorganisms?

Freeze dry the cells and freeze the cells at -70 degrees C in a solution that prevents formation of ice crystals.

What is the generation time measured during?

Log / Exponential phase.

What is the streak plate technique used for?

To spread a bacterial sample in a pattern that dilutes it.

Why is the exponential (log) phase important commercially?

It produces valuable primary and secondary metabolites.

What are the five stages of bacterial growth?

1. Lag; 2. Exponential; 3. Stationary; 4. Death; 5. Prolonged decline.

What best describes the dynamics of the phase of prolonged decline?

Although most of the population has died, a small number manage to persist.

Why are bacteria most sensitive to antimicrobial medications during the exponential phase?

There are the greatest numbers of bacteria present.

What do many antimicrobial medications target?

Processes most active when bacteria are growing.

How is microbial growth in a colony similar to growth in a liquid?

Cells in both situations compete with one another for available nutrients.

What are small molecules made by cells during log phase growth called?

Primary metabolites.

What are small molecules produced late in log phase growth called?

Secondary metabolites.

Which environmental factors have the most impact on microbial growth?

Temperature, pH, water availability, atmosphere.

How can some cells continue to multiply during stationary phase?

Some cells live off secondary metabolites or are unaffected by nutrient depletion.

At what temperature does Mycobacterium leprae grow best?

Below the usual core human body temperature of 37°C.

What term describes organisms that thrive in harsh environments?

Extremophiles.

What is an anaerobic environment?

An environment with little to no O2.

What describes a microbe that MUST have O2 to survive?

Obligate aerobes.

What are psychrotrophs commonly known for?

Causing refrigerated food spoilage.

Where could a facultative anaerobe be isolated?

Any of these locations: large intestine, surface of the skin, upper respiratory tract.

What is true regarding freezing as a preservation method?

It is a good method for preserving foods for long-term storage.

Where would you expect to find growth of an obligate anaerobe in a test tube?

Only at the bottom of the tube.

What is a microaerophile?

An aerobe that requires O2 at a concentration less than that in the atmosphere.

What is the causative agent of strep throat?

Streptococcus pyogenes.

What are reactive oxygen species (ROS)?

Products of oxygen metabolism in all aerobic organisms.

What describes facultative anaerobes?

They can grow with or without O2, but their growth is faster when O2 is available.

What is the pH preference for most microbes?

Near or at a pH of 7.

What is the role of autotrophs in the environment?

They convert inorganic carbon to an organic form through carbon fixation.

What is an example of an extreme halophile?

Archaea living in the salt flats of Utah.

Which five elements are major components of cell constituents?

Carbon, hydrogen, nitrogen, oxygen, sulfur.

What type of organism requires organic compounds for its carbon and energy needs?

Heterotroph.

What term describes organisms that use CO2 as a carbon source?

Autotrophs.

What is the process called when autotrophs convert inorganic carbon to organic form?

Carbon fixation.

What methods have been used to preserve food for hundreds of years?

Refrigerating them to inhibit microbial growth and sealing them in airtight containers.

What is the process by which some prokaryotes convert atmospheric nitrogen into ammonia?

Nitrogen fixation

What is an organism that must consume organic matter called?

Heterotroph

Which compounds require phosphorus as a component?

Nucleic acids

What do organisms that use inorganic carbon in the form of carbon dioxide called?

Autotrophs

What dictates the maximum level of microbial growth?

A limiting nutrient

Why could animals not survive without autotrophs?

Because they convert inorganic carbon to organic form, essential for animal life.

Which element do amino acids provide that sugar does not?

Nitrogen

What is a growth factor?

An organic compound that a microorganism cannot synthesize and must be provided in the growth medium.

What is the term for organisms that acquire their energy from chemical compounds?

Chemotrophs

What are trace elements?

Elements such as manganese and zinc needed by cells in very small quantities.

How do photoheterotrophs differ from photoautotrophs?

They differ in their carbon source.

What does a direct cell count determine?

The number of total cells in a sample.

What is an organism that gets its energy directly from sunlight called?

Phototroph or photoautotroph.

What is the viable plate method based on?

The principle that each colony represents one cell or colony-forming unit.

What is a reason to use membrane filtration as a viable cell count method?

To count cells present in dilute liquid samples.

What must be done before using a spectrophotometer to estimate cell number?

A test to determine the correlation between optical density and cell concentration.

What is the purpose of performing a serial dilution during the standard plate count method?

To achieve isolated bacterial colonies that can be reliably counted.

Which method involves sets of tubes and a table that gives an estimate of cell concentration?

Most probable number (MPN) method.

What is the principle of a Coulter counter and a flow cytometer?

Light is passed through a suspension of cells and measured by a detector.

What is the purpose of a flow cytometer in cell counting?

It can count total cells and specific subsets of cells.

Which of the following can be used for a direct cell count method?

Microscope.

What is the significance of viable cell counts?

They determine the number of cells capable of multiplying.

What is the definition of a serial dilution?

A sample being reduced in concentration through successive resuspension in the same volumes of diluent.

What is the advantage of using a flow cytometer for enumerating cells?

It can count a subset of dye-labeled cells.

What is the limiting nutrient in a lake with unwanted algal blooms?

Phosphate.

What are examples of chemotrophs?

Fungi and bacterial pathogens of humans.

What is the goal of a direct microscope count?

To count the total number of cells.

What is the role of phosphorous in microbial growth?

It is a necessary component for nucleic acids.

Why is it important to ensure that cells in a sample are not clumping together?

To accurately measure cell concentration.

What is the definition of viable cell counts in microbiology?

It refers to cells that are not only alive but also capable of reproduction.