Sep 29, 2025
LB agar plate recipe
- Jordan Ward1
- 1UC, Santa Cruz
Protocol Citation: Jordan Ward 2025. LB agar plate recipe. protocols.io https://dx.doi.org/10.17504/protocols.io.261gekx2yg47/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it's working
Created: September 21, 2025
Last Modified: September 29, 2025
Protocol Integer ID: 227830
Keywords: lb agar plate recipe ward lab recipe, making lb agar plate, lb agar plate
Funders Acknowledgements:
NIH
Grant ID: R35GM158317
Abstract
Ward lab recipe for making LB agar plates.
Troubleshooting
Weigh 10 g tryptone, 10 g sodium chloride (NaCl) and 5 g yeast extract and add to 975 ml milliQ water in a beaker with a magnetic stir bar. Mix until powder is dissolved.
Adjust pH to ~7.0 with 10N sodium hydroxide (~ 400 µl).
Pour into a graduated cylinder and bring to 1L with milliQ water.
Transfer to a bottle of the desired volume, add a magnetic stir bar and 15 g of bacto agar. Put on magnetic stirrer to mix.
Loosely screw on cap and autoclave on liquid cycle (55 min). Also include a 1 L nalgene beaker with a pouring spout. Cover the beaker opening with foil. Add autoclave tape to both.
Put on magnetic stir bar and cool to 55ºC (use infrared thermometer gun; we use this one https://www.amazon.com/Etekcity-Lasergrip-Thermometer-Temperature-Non-contact/dp/B00DMI62HM/ref=ast_sto_dp_puis_mod_primary_new?sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&th=1).
Spray down plate pouring area with 70% ethanol.
Set up a bunsen burner near plate pouring area after ethanol has evaporated.
While LB agar is cooling, set up stacks of 5-10 cm plastic petri dishes.
Optional: if making LB agar plates with antibiotics, add 1 ml of a 1000X stock and mix well on the magnetic stir plate.
- Wearing nitrile gloves, spray hands with 70% ethanol.
Transfer LB+agar to 1L Nalgene beaker and hand pour into 10 cm petri dishes. Keep Bunsen burner on nearby to prevent contaminants from landing in the media.
Let plates dry overnight. Then flip over and store at 4ºC. We store plates in a tub and mark the date that they were poured.