Pouring of Agar plates
1. Place the Petri plates to be poured right side up in front of you (if many plates are to be poured, you may want to set them up in stacks of three).
2. Obtain a bottle of melted (45°-50°) agar from the water bath. Carefully wipe the adhering water from the outside of the bottle so that, when you tip the bottle, this non-sterile water will not run into the sterile plate. Light a Bunsen burner and properly adjust the flame. Remove the cap of the bottle as illustrated in Figure A-3a. Lightly pass the lip of the bottle through the flame to create a temperature differential that prevents dust from dropping into the bottle. The lip of the bottle should already be sterile from the autoclaving procedure.
3. Pour 10-15 mls of molten agar into each plate (Fig A-3b). Stop just before the pool of agar touches the edges of the plate. With practice you will learn how to judge the proper amount by eye. Be careful to prevent the drip on the lip from running down onto the contaminated outer glass.
4. Immediately after pouring, cover the plates and use a firm circular motion to uniformly distribute the agar over the plate. Be quick or the agar will solidify before mixing.
5. Carefully slide the plates to an undisturbed area of the bench to solidify. Once solidified, invert the plates and incubate.
Figure A-3: (a) Removal of a bottle cap aseptically. Note how the rest of the hand is free to manipulate a pipette or plate lid. (b) Pouring agar into a plate. Note how the lid shields the agar from airborne contamination.