Ingredients:

• LB: 20 g/L
• Agar: 10 g/L (Note: not agarose)
• di water

Procedure:

1. Autoclave all the ingredients together in a glass bottle, loose cap and covered with alu foil, with 20 min liquid program (106). This takes about 1h in the autoclave.
2. Prepare the plates by labeling and ethanol cleaning a big enough surface.
3. Close the bottle and allow to cool down to 50-55ºC (colder will start to solidify, warmer might degrade the antibiotic).
4. Add the antibiotic to the bottle: 100 µg/ml for ampicillin, 50-100 µg/ml for spectinomycin.
5. Add 25-30 ml of the medium with antibiotic to each plate. Leave half open for about 2 h for cooling.
6. Close hte plates. Wrap the in alu foil (antibiotics are sensitive to light) and store the at 4ºC.