5 How Bacteria Grow Flashcards
(34 cards)
What is the term for bacterial replication?
Binary fission
______ ____: Time req’d for one binary fission event (i.e. a cell division)
Generation time (G)
T or F: Generation time (G) is constant.
F
- G is species dependent
- G is environment dependent
If we start with a single bacterial cell whose G=10 minutes, what will its population be after an 30 mins?
8
In a pop of bacteria, the number of bacterial cells will _____ after every generation
double
Name three ways to measure bacterial cell numbers.
- Direct microscopic count
- Turbidity
- Viable Count (“Plate Count”)
List the advantages and disadvantages of a direct microscopic count of bacterial cells.
Advantages: Simple and rapid
Disadvantages: Can’t distinguish b/w living and dead bacteria
When measuring bacterial cell numbers via turbidity, a higher turbidity is associated with a _____ number of cells.
greater
T or F: A large number of cells are needed to measure bacterial cell numbers via turbidity.
T
T or F: You can easily distinguish b/w living and dead bacteria using turbidity (as opposed to direct microscopic count)
F
Both living and dead cells will block light
In viable counts, how are the number of bacterial cells determined?
Bacterial cell pop is diluted, and then grown on growth media.
The number of colonies formed corresponds to the amount of bacteria (colony forming units) since “each living cell in a pop forms a colony on solid media”.
Specifically, # of bacteria (CFU) = # of colonies * dilution factor
If 1 mL of 1:100 dilution produces 20 colonies, how many bacteria were in the original culture?
20 * 100 = 2000 bacteria
T or F: Viable counts only measure number of LIVING cells.
T
T or F: Viable counts are very quick ways to determine cell numbers.
F
They usually take 18-24 hours, or even longer.
To carry out binary fission, bacteria need three things:
- Nutrients/water (at proper pH)
- Proper temperature
- Proper gaseous atmosphere
What does it mean for bacteria to “grow”?
To multiply.
T or F: All bacteria have the same nutrient needs.
F
Diff species req diff types of nutrients/organic cmpnds for growth.
T or F: The end products of metabolism vary greatly across diff bacterial species.
T
What is “water activity” (Aw)?
The amt of “free”, unbound water in a substance
T or F: Even spores cannot survive w/o water.
F
They CAN survive w/o water.
T or F: Bacteria have very liberal Aw requirements when it comes to growth.
F
They have STRICT requirements as to min and max water activity (i.e. free water) for growth
Most bacterial species only grow within an Aw range of ____ to ____.
0.90-0.99
Bacterial growth ain’t possible if Aw is less than ____.
0.50
Why are substances w/ Aw less than 0.50 not considered “sterile”?
There could still be spores present
