Ampicillin
Ampicillin is a β-lactam class antibiotic that acts by disrupting the synthesis of bacterial cell walls, derived from penicillin, and is used to select for cells with plasmids containing a gene producing beta-lactamase. It also helps to prevent unwanted growth of other cells on the plates. If it is warmed too much it is destroyed, so media has to cool to 60 C or below before adding ampicillin.
The final concentration of ampicillin should be 50 ug/ml or 0.05 mg/ml (divide by 1,000 to convert ug to mg). This 0.005 g per 100 ml solution. A 100X stock can be made up with 0.5 g / 100 ml (of 50% EtOH to promote dissolving the AMP powder) and 1 ml stock added to 99 ml solution. (Aliquot the 100X AMP solution and keep frozen so you only have to take out and thaw a few milliliters at a time.)
