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Preparing an Agar Plate

Agar plates are used in microbiology to grow and culture bacteria for study. The agar is a gelatin that acts as a surface and a source of nutrients for the bacteria colonies to grow on. Scientists will use different ingredients in agar to grow different types of bacteria, and study the effects of various compounds, such as proteins and medicines, on bacteria growth.

Preparing an agar plate from the local bacteria found in your body is a fun and easy science experiment that can be done at home, and can make for a great science fair project.


What you’ll need:

  • Petri dish
  • Bacteriological agar
  • Q-tip

Agar will either arrive pre-mixed in its gelatin form, or as a powder that can be mixed with water. In the case of pre-mixed agar, the media simply needs to be heated up in an autoclave, hot water bath, or microwave until the agar can flow freely. If the agar needs to be mixed, simply add the powder to water and mix. The proper mix ratios will vary depending on the type of agar used, so be sure to keep an eye on the instructions to get the right mixture.

Once the agar is in a state where it can run freely, pour it into a petri dish, making sure to cover the entire surface of the dish. Allow the agar to dry while keeping the lid on the plate. Keeping the lid on as much as possible will reduce the risk of the petri dish becoming contaminated and growing errant bacteria.

Once the surface has solidified to a gelatin, swab the inside of your cheek with a q-tip and brush it gently on the surface of the agar, making sure to coat the agar without breaking the surface. The bacteria from the q-tip will absorb nutrients from the agar and begin to propagate. Place the lid back on the plate and store upside down. After some time (hours to days), bacterial colonies should begin to grow on the agar’s surface.

This experiment can be done using bacteria from a variety of sources. Instead of your cheek, try making plates of your hands before and after washing, or testing the five-second rule. You can even use your agar plate to make art!

Happy growing!


Related Links

Agar on hBARSCI

Petri dishes on hBARSCI

Microbiology Science Fair Kit - a small kit to make a few plates

Introduction to Microbiology Kit - a full kit for a classroom

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