Bacterial growth in the lab - Lag phase
- Bacteria adapt to growth conditions
- Maturing but not dividing
- Synthesis of genetic material, enzymes and other molecules occurs
Bacterial growth in the lab - Exponential phase
- Bacteria are adapted to environment
- Rate of binary fission is at max
- Grows exponentially
Bacterial growth in the lab - Stationary phase
- Growth rate and death rate are equal
- There is a depletion of nutrients and buildup of waste products
Bacterial growth in the lab - Death phase
- Bacteria die or become smaller due to lack of nutrients and accumulation of deleterious mutations
What happens when dilute bacterial populations are spread on an agar plate?
- Individual colonies arise upon incubation
- Each colony on the plate is a clonal population derived from an individual cell
What happens when enumerating phage or virus?
They infect a monolayer of cells, lysing patches of neighboring cells and forming clear zones called plaques
What is a plate assay?
A method used to quantify microbes
Step 1 - plating assay
Take a known volume of stock and place it in a known volume of distilled water
Step 2 - plating assay
Take a known volume of the first dilution and place it in a known volume of distilled water
Step 3 - plating assay
The process is continued until the desired dilution is reached
Step 4 - plating assay
- Multiple dilutions are used to inoculate media or monolayers
- The more concentrated the stock, the more plaques or colonies that form
What is a plaque assay and how is it performed?
- A plaque assay is a plating assay used for viruses
- Viruses are added to a plate with a monolayer of host cells and covered with a gel layer to stop viral diffusion
- During incubation, infected cells lyse and release new viruses, creating clear circular zones of infected cells called plaques
How is the original concentration of a virus or bacterial culture determined in a plating assay?
It’s calculated in PFU/mL (for viruses) or CFU/mL (for bacteria) by counting the number of plaques or colonies and using the dilution factor
Plating assay equation
PFU/mL = (Number of plaques) / [(Dilution) × (Volume of diluted virus added)]
What is a hemocytometer?
It’s a specially designed microscope slide and coverslip used to count eukaryotic cells.
How is cell number determined using a hemocytometer?
- The number of cells is calculated using the chamber’s volume and any dilutions made.
- The sample must be fairly dense for accurate results.
What is spectrophotometry used for in microbiology?
It measures cell numbers by passing light of a specific wavelength through a suspension of cells and detecting how much light is absorbed.
How does cell population affect light absorption in spectrophotometry?
As the number of cells goes up, the liquid gets cloudier, so less light passes through and more is absorbed. The absorbance is compared to a standard curve to find the cell number.
-
Module 1: Section 124
-
Module 1: Section 236
-
Module 2: Section 1A26
-
Module 2: Section 1B54
-
Module 2: Section 1C8
-
Module 2: Section 1D7
-
Module 2: Section 2A16
-
Module 2: Section 2B6
-
Module 2: Section 2C5
-
Module 2: Section 2D12
-
Module 3: Section 1A15
-
Module 3: Section 1B19
-
Module 3: Section 1C16
-
Module 3: Section 2A18
-
Module 3: Section 2B22
-
Module 3: Section 2C31
-
Module 3: Section 2D23
-
Module 3: Section 2E14
-
Module 4: Section 1A24
-
Module 4: Section 1B24
-
Module 4: Section 2A15
-
Module 4: Section 2B14
-
Module 4: Section 3A34
-
Module 4: Section 3B31
-
Module 4: Section 3C21
-
Module 5: Section 1A15
-
Module 5: Section 1B9
-
Module 5: Section 1C14
-
Module 5: Section 2A30
-
Module 5: Section 2B13
-
Module 5: Section 2C32
-
Module 6: Section 1A15
-
Module 6: Section 1B24
-
Module 6: Section 1C14
-
Module 6: Section 2A14
-
Module 6: Section 2B32
