LB medium (Luria-Bertani, Miller) recipe
The basic medium for growing E. coli; add agar for LB plates.
🧮 Volume calculator
| Component | Amount | Final concentration (1X) |
|---|---|---|
| Tryptone | 5 g | 1% |
| Yeast extract | 2.5 g | 0.5% |
| NaCl | 5 g | 1% (171 mM) |
| Agar (plates only) | 7.5 g | 1.5% |
| Water (distilled) | to final volume |
Steps
- Dissolve the components and bring to volume (pH ≈ 7.0, usually not adjusted).
- Autoclave at 121 °C for 20 min.
- Add antibiotics after cooling to about 50–55 °C.
- Pour about 20–25 mL per plate, let set and store inverted at 4 °C.
Good to know
- Lennox LB uses 5 g/L NaCl and Luria LB 0.5 g/L; use low-salt LB for salt-sensitive antibiotics (e.g. blasticidin).
FAQ
How long do antibiotic plates keep?
Usually 2–4 weeks at 4 °C; ampicillin plates lose potency faster, so use them fresh.
This is a widely used standard composition. Amounts depend on the hydrate form and purity of your reagents — check the formula weight (FW) on the bottle and follow your institution's safety rules and the manufacturers' instructions.