When cultivating bacterial cultures for the purposes of recombinant protein expression, antibiotics are necessary to provide selection pressure for the expression vector harbored by the bacteria. Many commercially available vectors provide kanamycin resistance. Kanamycin is usually used at a concentration of 25-50 µg/mL. Many people prefer kanamycin over ampillicin due to its greater long-term stability.
For preparation of 10 mL of 50 mg/mL kanamycin
1) Dissolve 500 mg kanamycin sulfate powder in 10 mL ddH2O.
2) Filter sterilize antibiotic solution using a 0.2 µm syringe filter.
3) Aliquot (500 µL - 1 mL aliquots are useful) and store at -20 °C until use.
NOTE: It is best to avoid repeated freeze/thaw cycles of the kanamycin aliquots.