To prepare an agar culture medium, one must first sterilize empty petri dishes by boiling them and allowing them to dry upside down. Agar powder is then prepared by mixing it with water in a microwave according to standard directions. Bottled agar formula is also warmed in the microwave with the cap loosened but not removed. Once the agar is liquid, petri dish lids are cracked open and the agar is carefully poured into the dishes under the lid to prevent contamination, setting to a thickness of 1/8 inch before storing upside down once solidified.

1. How to Prepare an Agar Culture
Medium

2. Objectives:
At the end of this presentation, one must be able to:
 Prepare an Agar Petri dish using the right
procedures
 Identify the materials used in the preparation

3. Introduction:
Agar is a gelatinous substance perfect for
biological experiments since it holds up bacteria and
does not disintegrate quickly. You can use a bottle of
specially prepared liquid, tablet or powder to make
your Agar plate.

4. Procedures:
 1 Begin by sterilizing the Petri dishes. Place in a
bath of boiling water and allow them to dry upside
down on a sanitized drying rack or lab work bench.
If the Petri dishes are still enclosed in the original
packaging, leave them until ready to use. For 500
milliliters of agar mixture, you can fill 25 Petri
dishes.

5. Procedures:
 2 Prepare agar powder by placing it in the
microwave with the appropriate amount of water.
The label should provide specific directions
although 6.9 grams to 500 ml of water is standard.
For agar tablets, 10 tablets dissolved in two cups of
water is standard.

6. Procedures:
 3 Treat bottled agar formula carefully by loosening
the bottle cap (but not removing) before placing in
the microwave to warm and soften into a liquid state.
Sterilize the bottle after microwaving by placing the
neck of the bottle over an open flame a few times to
ensure any airborne germs are eradicated before
proceeding to plate making.

7. Procedures:
 4 Place the Petri dishes the right way up and crack
but do not remove the lids. This is to prepare them
for individual handling when the other hand is
holding the agar mixture in a suitable pouring
vessel such as a glass pitcher.
 5 Gently lift the lid of the Petri dish with one hand
and hover the lid immediately over the bottom dish
to remove any chance of airborne germs entering.

8. Procedures:
 6 Pour an amount of agar liquid into each dish as
you hover the lid. About 1/8 inch is the standard
thickness of the agar liquid.
 7 Allow the agar to set into the dishes by leaving
them on a flat, clean surface to dry in room
temperature. Secure lids once set and store upside
down.