Solid LB with 100 µg/mL Ampicillin

• 1. Add 15 g of agar to 1 L of LB liquid medium and stir to mix. Autoclave to sterilize the solution and melt the agar. Swirl the flask to mix. (Do not shake.) Cool the solution to 55°C.

• 2. Add 10 mL of ampicillin stock solution (10 mg/mL) and swirl the flask to mix.

• 3. Pour ∼25 mL of solution per dish into 10-cm Petri dishes.

• 4. Once the medium has solidified, prop open the lid of the plates inside a biological safety hood. Let stand until condensation inside the lid has evaporated. Invert the plates and store them at 4°C until use.

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