Antibiotic stock solutions
All stocks are 1000× — add 1 mL stock per 1 L medium for the working concentration.
Reference table
| Antibiotic | Stock (1000×) | Working conc. | Solvent | Filter? | Storage |
|---|---|---|---|---|---|
| Ampicillin | 100 mg/mL | 100 µg/mL | H₂O | 0.22 µm | −20 °C |
| Carbenicillin | 100 mg/mL | 100 µg/mL | H₂O | 0.22 µm | −20 °C |
| Kanamycin | 50 mg/mL | 50 µg/mL | H₂O | 0.22 µm | −20 °C |
| Chloramphenicol | 34 mg/mL | 34 µg/mL | EtOH (100%) | No | −20 °C |
| Spectinomycin | 100 mg/mL | 100 µg/mL | H₂O | 0.22 µm | −20 °C |
| Tetracycline | 10 mg/mL | 10 µg/mL | 70% EtOH | No | −20 °C, dark |
| Gentamicin | 10 mg/mL | 10 µg/mL | H₂O | 0.22 µm | −20 °C |
| Streptomycin | 50 mg/mL | 50 µg/mL | H₂O | 0.22 µm | −20 °C |
| Erythromycin | 200 mg/mL | 200 µg/mL | EtOH (100%) | No | −20 °C |
| IPTG | 1 M | 0.1–1 mM | H₂O | 0.22 µm | −20 °C |
| X-Gal | 20 mg/mL | 40 µg/mL | DMF | No | −20 °C, dark |
Procedure (general)
- Weigh the antibiotic on weigh paper. Wear gloves and a mask.
- Dissolve in the appropriate solvent. For aqueous stocks, vortex briefly; for ethanol stocks, dissolve fully (may take inversion + light vortex).
- For aqueous stocks: filter through a 0.22 µm syringe filter. Do NOT autoclave antibiotics.
- Aliquot 0.5–1 mL into labelled cryotubes. Avoid repeat freeze-thaw — discard after ~5 cycles.
- Store at −20 °C. Tetracycline and X-Gal need protection from light (foil-wrap aliquots).
Important notes
- Add antibiotic only to medium < 55 °C — heat destroys most antibiotics.
- Carbenicillin is more stable than ampicillin in long incubations; otherwise interchangeable.
- For mammalian cell lines, use cell-culture-grade antibiotics at recommended doses (e.g., G418 0.5–1 mg/mL, puromycin 1–5 µg/mL, blasticidin 5–10 µg/mL).