Microbiology - Ch. 6 - Microbial Growth

Front 1

Describe a psychrotroph.

Back 1

One type of psychrophile responsible for low-temperature food spoilage.

Can grow at 0 degrees but has higher optimum temps (20-30).

Front 2

Define psychrophile.

Back 2

One of the three main groups - "Cold-loving microbes."

Includes microbes that can grow at 0 degrees but have an optimum temp of 15 degrees C. The other group can grow at 0 degrees but has an optimal temp of 20-30 degrees (psychrotrophs).

Front 3

In what pH range to microbes grow best?

Back 3

6.5-7.5 (near neutrality)

Very few bacteria grow at a pH below 4.0

Front 4

Can bacteria survive at pH 1?

Back 4

Yes, there is a chemoautotrophic bacteria found in the drainage water of coal mines that survives.

Front 5

What is the optimal pH range of molds & yeasts?

Back 5

5-6

Front 6

Regarding pH, what is used to preserve foods?

Back 6

Acid conditions. Alkalinity also inhibits microbial growth, but isn't used to preserve foods.

Front 7

What are buffers?

Back 7

Chemicals included in bacterial growth medium that neutralize the acids bacteria produce and maintain the proper pH.

Front 8

Define hypertonic solution.

Back 8

A solution that has a higher concentration of solutes than in the cell.

Front 9

What do you know about osmotic pressure?

Back 9

When it comes to solutions, water will always move from the area of low solute concentration to the area of high solute concentration.

High osmotic pressure means the cell will lose water.

Front 10

What is the difference between an aerobe and an obligate aerobe?

Back 10

Aerobes are microbes that use molecular oxygen.

Obligate aerobes are organisms that REQUIRE oxygen to live.

Front 11

What is a facultative anaerobe?

Back 11

Aerobic bacteria that is cablable of using oxygen when it is present, but can also continue to grow without it by using fermentation or anaerobic respiration.

Front 12

What is an obligate anaerobe?

Back 12

Bacteria that are unable to use molecular oxygen for energy-yielding reactions. Most are HARMED by oxygen

Front 13

What is a aerotolerant anaerobe?

Back 13

Bacteria that cannot use oxygen for growth, but can tolerate it fairly well.

Front 14

What is a culture medium?

Back 14

A nutrient material prepared for the growth of microorganisms in a laboratory.

Front 15

What are the factors to consider in a culture media?

Back 15

Proper nutrients for the microbe.
Sufficient moisture.
Properly adjusted pH.
Suitable level of oxygen.
Initially must be sterile.
Proper incubation temperature.

Front 16

What is agar?

Back 16

A complex polysaccharide derved from marine alga. A solidfying agent used in culture media.

Front 17

What makes agar of great use in culture media?

Back 17

* Few microbes can degrade it, so stays solid
* Melts at boiling point of water
* Remains liquid until temp drops to 40 degrees celcius
* Can be incubated to temperatures approaching 100 degrees before it liquifies (useful for thermophilic bacteria)

Front 18

What is a chemically defined media?

Back 18

A chemically defined medium is one whose exact chemical composition is known.

Front 19

What must a culture media provide?

Back 19

An energy source.
Sources of carbon, nitrogen, sulfur, phosphorus, growth factors.

Front 20

What does it mean when an organism is fastidious?

Back 20

It requires many growth factors.

Front 21

What is a complex media?

Back 21

Media whose exact chemical composition varies slightly from batch to batch.

Used for heterotrophic bacteria & fungi.

Front 22

What is a peptone?

Back 22

A shorter chain of amino acids, produced when protein is partially digested by acids or enzymes.

Front 23

What is reducing media?

Back 23

Specia media used with anaerobic bacteria. Has sodium thiglycolate, which combines with dissolved oxygen and depletes oxygen in the culture media.

Used in tightly capped test tubes.

Front 24

What are selective media?

Back 24

Media that are designed to suppress the growth of unwanted bacteria & encourage the growth of the desired microbes.

Front 25

What are differential media?

Back 25

Media that make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate.

Front 26

How do you calculate generation time?

Back 26

Initial # of cells x 2^number of generations

Front 27

What is the stationary phase?

Back 27

The phase of bacterial growth in which the number of new cells created equals the number of cells dying.

Front 28

What is the lag phase?

Back 28

The phase of bacterial growth in which there is little or no cell division (because cells do not immediately reproduce in a new medium)

Front 29

What is the log phase?

Back 29

The phase of bacterial growth when cells are most active and generation time reaches a constant minimum.

Front 30

What is the death phase?

Back 30

The phase of bacterial growth when the number of deaths exceeds the number of new cells formed. (aka Logarithmic decline phase)