Help:How to make agar

Preparing agar

  1. Prepare LB agar according to manufacturer's instructions (e.g. 35g of agar in 1L diH2O for Difco LB Lennox Agar). Adjust pH to 7.5 if necessary with 1M NaOH.
  2. Autoclave media (with caps loosened!) for 20 minutes at 121 degrees
  3. Cool down to 55 degrees. Since autoclaved agar cools down slowly, a good way to do this is prepare and autoclave it in the morning then leave it in a 55 degree water bath. Don't try to cool it down quickly because the glass may shatter.
  4. Once it's cool enough (50-60 degrees) - add antibiotics: 1mL per litre for Ampicillin, Chloramphenicol, Kanamycin and 3mL per litre for Tetracycline. (concentrations of liquid stocks: Amp- 100mg/ml, Cm- 35mg/ml, Kan- 50mg/ml, Tet- 5mg/ml.)
  5. Swirl to mix; try not to make many bubbles.
  6. Fill petri dishes or screw-cap tube half-full with agar and cap. Once set, store in refrigerator for future use.
  • Don't forget to label the plates/tubes with the appropriate antibiotic!
We have a standard color key for our antibiotics:
Orange denotes ampicillin,
Red denotes kanamycin,
Green denotes chloramphenicol,
Yellow denotes tetracycline.
These are Ampicillin plates
These are Ampicillin-Kanamycin plates