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30 Cards in this Set

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

Can grow at 0 degrees but has higher optimum temps (20-30).
Define psychrophile.
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).
In what pH range to microbes grow best?
6.5-7.5 (near neutrality)

Very few bacteria grow at a pH below 4.0
Can bacteria survive at pH 1?
Yes, there is a chemoautotrophic bacteria found in the drainage water of coal mines that survives.
What is the optimal pH range of molds & yeasts?
Regarding pH, what is used to preserve foods?
Acid conditions. Alkalinity also inhibits microbial growth, but isn't used to preserve foods.
What are buffers?
Chemicals included in bacterial growth medium that neutralize the acids bacteria produce and maintain the proper pH.
Define hypertonic solution.
A solution that has a higher concentration of solutes than in the cell.
What do you know about osmotic pressure?
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.
What is the difference between an aerobe and an obligate aerobe?
Aerobes are microbes that use molecular oxygen.

Obligate aerobes are organisms that REQUIRE oxygen to live.
What is a facultative anaerobe?
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.
What is an obligate anaerobe?
Bacteria that are unable to use molecular oxygen for energy-yielding reactions. Most are HARMED by oxygen
What is a aerotolerant anaerobe?
Bacteria that cannot use oxygen for growth, but can tolerate it fairly well.
What is a culture medium?
A nutrient material prepared for the growth of microorganisms in a laboratory.
What are the factors to consider in a culture media?
Proper nutrients for the microbe.
Sufficient moisture.
Properly adjusted pH.
Suitable level of oxygen.
Initially must be sterile.
Proper incubation temperature.
What is agar?
A complex polysaccharide derved from marine alga. A solidfying agent used in culture media.
What makes agar of great use in culture media?
* 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)
What is a chemically defined media?
A chemically defined medium is one whose exact chemical composition is known.
What must a culture media provide?
An energy source.
Sources of carbon, nitrogen, sulfur, phosphorus, growth factors.
What does it mean when an organism is fastidious?
It requires many growth factors.
What is a complex media?
Media whose exact chemical composition varies slightly from batch to batch.

Used for heterotrophic bacteria & fungi.
What is a peptone?
A shorter chain of amino acids, produced when protein is partially digested by acids or enzymes.
What is reducing media?
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.
What are selective media?
Media that are designed to suppress the growth of unwanted bacteria & encourage the growth of the desired microbes.
What are differential media?
Media that make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate.
How do you calculate generation time?
Initial # of cells x 2^number of generations
What is the stationary phase?
The phase of bacterial growth in which the number of new cells created equals the number of cells dying.
What is the lag phase?
The phase of bacterial growth in which there is little or no cell division (because cells do not immediately reproduce in a new medium)
What is the log phase?
The phase of bacterial growth when cells are most active and generation time reaches a constant minimum.
What is the death phase?
The phase of bacterial growth when the number of deaths exceeds the number of new cells formed. (aka Logarithmic decline phase)