How to Prepare a Petri Dish Before Growing Bacteria

How to Prepare Petri Dish Before Growing Bacteria

1. Prepare the agar.

Agar is a gelatinous substance used for the cultivation of bacteria. Made of a type of red algae, it provides an ideal growth surface for various types of bacteria. Some types of agar contain additional nutrients (such as sheep’s blood) that promote the growth of more active bacteria.
The simplest type of agar used in this experiment is powdered nutritional agar medium. You will need as much agar as needed, but use no less than 1.2 grams (1/2 teaspoon) of powdered agar per 10 centimeters (3.9 inches) of petri dish. you use.
In a baking dish or bowl, add 1.2 grams (1/2 teaspoon) of nutrient agar powder to 60 ml (0.25 c) of hot water and stir. Multiply these quantities by the number of petri dishes you plan to use.
Place the bowl or dish in the microwave and boil for at least 1 minute making sure the agar solution does not boil.
When the solution is ready, the agar powder should be completely dissolved and the liquid should be clear.
Allow the agar solution to cool for a few minutes before proceeding. I don’t want to burn myself!

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2. Prepare a petri dish.

Petri dishes are small, flat-bottomed containers made of clear glass or plastic. They have two halves (top and bottom) and slots on top of each other. This protects the contents from unwanted polluted air, but also allows gas produced by bacteria to escape.
Petri dishes should be completely sterilized before being used for bacterial growth. Otherwise, it may affect the experimental results. Newly purchased petri dishes should be pre-sterilized and sealed in plastic wrap.
Remove the petri dish from the packaging and divide it into two parts. Very carefully, pour the hot agar solution into the bottom half of the Petri dish, just enough to form a layer on the bottom of the dish. Work in the presence of high flame candles or Bunsen burners to reduce pollution.
Promptly replace the top half of the Petri dish to prevent airborne bacteria from contaminating the experiment. Leave the petri dish for 30 minutes to 2 hours until the agar solution cools and hardens (when ready it looks like a set of jero).

3. Refrigerate Petri dish until ready to use.

If you are not planning to use the petri dish with agar immediately, you should store it in the refrigerator until you are ready to continue the experiment.
Keeping the petri dish in the fridge will prevent the water in the dish from evaporating (bacteria need a moist environment to grow). In addition, the surface of the agar is slightly hardened to prevent crevices and gouges when transferring bacterial samples.
When storing petri dishes in the refrigerator, the dishes should be placed upside down. This helps prevent condensation on the lid from falling off and disturbing the grow surface.
Petri dishes filled with agar can be stored in the refrigerator for several months. When ready to use, remove from refrigerator and allow to warm to room temperature before adding sample.