Pouring an agar plate
Refer to Aseptic techniques before starting this or any other microbiology practical work.
The instructions are for right-handed workers – turn them around if you are left-handed!
Health & Safety and Technical notes
1 Use a water bath at 50 °C to store bottles of molten agar.
2 Use plates as soon as possible after pouring. Store in sealed plastic bags to prevent the agar from drying out if they are not going to be used straight away.
Notes based on information in 'Basic practical microbiology' © Society for General Microbiology.
a Light a Bunsen burner and set it to a hot, roaring flame.
b Collect a bottle of sterile molten nutrient agar from the water bath.
c Hold the cap of the bottle firmly between the little finger of your left hand and the palm of your left hand. Unscrew the bottle by turning with your right hand. Leave the cap gripped by the little finger of the left hand.
d Flame the neck of the bottle.
e Lift the lid of the Petri dish slightly with your left hand and pour the sterile molten agar into the Petri dish.
f If pouring a series of plates, flame the neck of the bottle again and replace the cap if pausing. If pouring a single plate from a measured amount in a McCartney/ Universal bottle, place the empty bottle directly in a basin of hot water to make it easier to wash up.
g Gently rotate the dish to ensure that the medium covers the base of the dish evenly. The base of the plate must be covered, agar must not touch the lid of the plate, and the surface must be smooth with no bubbles. If there are bubbles, you can try flaming the agar surface very briefly to disperse them – but this carries the risk of melting the Petri dish!
h Allow the plate to solidify (Note 1).
Microbiology teacher resources
Society for General Microbiology – source of Basic Practical Microbiology, an excellent manual of laboratory techniques and Practical Microbiology for Secondary Schools, a selection of tried and tested practicals using microorganisms.
MiSAC (Microbiology in Schools Advisory Committee) is supported by the Society for General Microbiology (see above) and their websites include more safety information and a link to ask for advice by email.
(Websites accessed October 2011)