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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.

  1. 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.

  2. 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:

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