Bacterial Growth And Measuring It Flashcards
What is generation time
Time needed for 1 cell to double
Eg 20 mins = 2 cells formed
What is the word to describe growth of bacteria
Exponential - doubles at constant time
Name the 4 phases in the growth cycle
1- lag
2- exponential
3- stationary
4- death
Explain the lag phase
There is slow growth due to new conditions
New metabolites and enzymes synthesised for growth
Explain exponential phase
Rapid growth with abundant nutrients and enzymes available for growth
Explain the stationary phase
Nutrients start to depleat and build up of toxic products
The exponential growth is constant with death rate
What happens in the death phase
Death overtakes exponential growth
No more nutrients
Toxic byproducts produced by bacteria
Name the 4 ways to measure bacterial growth
1- plating method
2- turbidity/ optical density
3- direct counting
4- flow cytometry/ FACS
Explain the plating method
Bacteria in culture placed in serial dilution plates
This makes them easier to count
To find out the amount in original you do
Dilution factor x 10 x count = original
Which cells does the plating method count
ONLY VIABLE / LIVE cells
What is an advantage with the plating method
You can maintain conditions to match the pathogen you want to grow and avoid others growing
What is a disadvantage of plating methods
You can’t count clusters of cells making it inaccurate
How does the turbidity/ optical density method work
Light shines into a filter and slide with cells on it
If cells are present and they move then will move and diffract light
Scattered light DOESNT pass through photo cell
Higher absorbance on spectrophotometer if more bacteria present
Why is optical density method good
Not destructive to the bacteria and easy to measure
Why is turbidity inaccurate in measuring viable cells
They can count dead cells too and other particles which scatter light
