How To Grow Bacteria on Agar Plates
Growing bacteria, or other microorganisms, on agar plates is a common step in microbiology experiments. There are two methods for inoculating (putting the bacteria on) agar plates: quadrant streaking and spread plating. Which one you choose depends on what you want to do after.
- Quadrant Streaking Bacteria or Fungi
The quadrant streaking technique is used to isolate single colonies of one or more types of bacteria or fungi. To get started, you will need:
- A clean, sterile work area
- Agar plates appropriate for growing the bacteria or fungi you are trying to isolate
- Sterile tools, like a loop or swab sticks, for swiping the microorganisms across the agar
- A starting colony or culture to work from
How to quadrant streak bacteria and fungi is shown step-by-step in this video:
If you use the quadrant streak technique to isolate unknown microorganisms, our How to Identify Bacterial Colonies resource can help you figure out what each bacterial colony is.
- Spread Plate Technique for Bacteria and Fungi
The spread plate technique is used to grow a continuous lawn of bacteria or fungi on an agar plate. To get started, you will need:
- A clean, sterile work area
- Agar plates appropriate for growing the bacteria or fungi you are trying to grow
- A sterile spreader or sterile glass beads
- A starting culture to work from
This video shows step-by-step how to do the spread plate technique:
The spread plate technique is also used to plate dilutions of a bacterial or fungal sample when you are trying to estimate the number of bacteria (or fungi) in the sample. The quantity of bacteria/fungi is reported in terms of colony forming units (CFU).
This video explains more about what CFUs are and how to calculate them:
