How to grow bacteria on agar plates

Written by andrew youngker
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How to grow bacteria on agar plates
Protective gloves should be worn when handling potentially hazardous bacteria. (Bacteria Colonies image by ggw from

Agar plates are commonly used in laboratories to grow bacteria for research purposes. The agar on the plate serves only as a medium to hold the bacteria, while added nutrients help the bacteria grow. Laboratories may use ready-made plates because they are consistent and faster than preparing plates from scratch. Incubators provide a consistent environment for bacteria to grow at their optimum capacity. Some bacteria have specific nutrition requirements that may affect growth. Blood agar is a commonly use medium for both nutrients and the ease in detecting bacterial colonies.

Skill level:

Things you need

  • Marker
  • Cotton swabs
  • Masking tape
  • Incubator

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  1. 1

    Take the agar plates from refrigeration and allow the plates to come to room temperature. This prevents the bacteria from being stressed during the process.

  2. 2

    Mark the plates with any identifying information near the outer edge of the agar plate. Writing on the plate with the agar prevents any confusion if the lids are misplaced.

  3. 3

    Swab the target surface of interest with a clean cotton swab.

  4. 4

    Open the plate lid and lightly swab the agar using a brushing motion. Limit the amount of time the agar is exposed for contamination reasons.

  5. 5

    Tape the plates in groups, if using more than one for an experiment, and place lid side down.

  6. 6

    Place the stack of plates in an incubator, lid side down, set the incubator temperature to around 37.8 degrees Celsius (2.78 degrees C Celsius). Any dark space that is not over direct heat can be used if you do not have an incubator.

  7. 7

    Check the plates every day for bacterial colony growth.

Tips and warnings

  • Store plates with lid side down to keep condensation from dropping onto the growing bacteria.
  • Normally harmless bacteria may be harmful when grown into millions of cells.
  • Incubators that are too hot will cause bacteria not to grow.

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