Materials: Nutrient Agar Powder
distilled water
250 ml flask
aluminum foil
sterile tape
sterile plastic petri dishes
autoclave or microwave
marker
incubator
Note: Keep sterile petri dishes closed until ready to pour agar into them.
Air-borne contaminants can easily invade an open petri dish.
Procedure:
1. Measure agar and distilled water into clean flask or beaker.
Recipe: Agar + Distilled Water = Yield
Agar
2.3 g
+ Distilled Water
100 ml
= Yield
5 plates
2. Mix powder and water in 250 ml flask.
3. Cover with aluminum foil and a piece of sterile indicator tape and
place in the autoclave.
4. Autoclave for 20 minutes. Make sure the autoclave is set to SLOW
EXHAUST. Ask for help before starting the autoclave.
5. Wear heat-resistant gloves to remove the flasks from the autoclave.
6. Allow the solution to cool to about 60 degrees before pouring.
NOTE: This process can be done beforehand, and the agar
allowed to harden in the flask. If this is the starting point, the
aluminum foil should be removed and the flask placed in the
MICROWAVE oven. Heat for 30 seconds at a time, with swirling
in between (WEAR HOT GLOVES) until the mixture is uniform.
Let cool and proceed.
7. Pour enough melted agar into each sterile plastic petri dish to cover
the bottom - about 1/8" to 1/4" deep. Replace the lid immediately.
8. Place agar plates on a counter top to cool and set. Agar medium will
set like stiff gelatin at room temperature.
9. The agar medium is now ready for storage or use.
Storage: Stack agar plates upside down in the refrigerator. Do Not
Freeze! The purpose of placing the plates upside down is to prevent
condensation from dripping down onto the agar surface which could then
facilitate movement of organisms between colonies.
What is on your hands?
1. Allow them to warm to room temperature if they have been in the
refrigerator
2. Uncover each agar plate just long enough to press your palm or
fingers onto the agar surface..
3. Cover the Petri dish immediately and turn upside down.
4. Label the dish with your name ON THE BOTTOM.
Incubation:
1. Turn the plates upside down and put them in a warm place. The
ideal temperature for incubation is 32° C or 90° F. Bacterial growth
should start to become visible in about 2 -3 days.