Here we have two common preparations for agar media; the Potato Dextrose Agar (PDA) and Malt Extract Agar (MEA). The follow example details the process of making 1 litre of PDA as this is the most accessible low cost method. This amount is enough to pour 20 x 80mm petri dishes.
MEA
- 20g Agar agar
- 20g Malt extract
- 2g yeast (optional
PDA
- 300g – 400g potato
- 20g Agar agar
- 10g dextrose powder
- 2g yeast (optional)
- The broth should be about 1litre in volume once boiled and strained
Materials:
- Potatoes
- Agar agar
- 2-3l water
- Glucose Dextrose Powder
Equipment:
- erlenmeyer flask / narrow, long neck bottle
- cotton wool or polyester filling
- pressure cooker
- alcohol solution in spray bottle
- infra red thermometer
- 20 x 80mm petri dishes (just this example, you could us other sizes obviously)
- latex gloves
- face mask
- tyvex sleeves or hazmat suit
Overview:
- Take a potato, cut into chunks or shred
- add to pot with 2 – 3l of water (enough to make 1litre when boiled down)
- boil for one hour, don’t let it boil over
- strain liquid
- pour into flask / bottle
- add agar and dextrose powder
- 15 psi 30 minutes
- when below 3psi move pressure in sterilised area, ideally in front of HEPA filter (laminar flow)
- open just above 0psi
- remove with sterilise paper towel
- check temperature with infra red thermometer pouring temperature is 38c
- while waiting, wipe down outside of petri dishes bag with Alcohol Solution
- carefully open bottom of the bag with scalpul / scissors
- Place stack on the work surface and remove bag
- When ready to pour, swirl mixture
- carefully lift the lid from the petri dish at the bottom of the stack. Make sure your fingers just touch the top of the sides of the lid.
- Pour agar
- Place lid down, lift up the lid of petri dishes second from the bottom and so on until all petri dishes are filled
- wait until cooled below 20c and use, or wrap with para film and refrigerate for future use