Estimated time required to finish the preparation is about 2 hours for 1 liter of LB agar plates (about 30 of them)
1. To a flask of volume at least 4-L, add:
10g Tryptone
5g Yeast Extract
5g NaCl
2. Add about 800mL of dH2O and dissolve the big chunks and stir with a magnetic bar until it's all dissolved.
3. Add 400ul of 5N NaOH and stir.
4. Remove the magnetic stir bar and pour the solution into a clean 1000 ml graduated cylinder. Use dH2O to bring the liquid level to 1000 ml.
5. Pour the medium back to the flask and add the stir bar.
6. Add 15g of granulated agar to the liquid and stir for about a minute.
7. Remove the stir bar. Cover the flask with aluminum foil and autoclave for 20 min using the liquid cycle.
8. Cool down the medium until it's cool enough to be hold by hands (about 40oC).
9. Spray and wipe the bench with 95% ethanol.
10. Open a bag of sterile 3" empty plates and place them in stacks of 10 plates with the lids up (Note: save the bag for later storage. Label the plates for proper identification:
LB only - single vertical black band
LB + Ampicillin - (optional black band) single vertical red band
LB + Chloramphenicol - not sure
LB + Kanamycin - (optional black band) single vertical green band
11. When it's cooled down enough, add the appropriate amount of antibiotic(s) to the medium and swirl to mix:
100ug/mL Ampicillin
34ug/mL Chloramphenicol
10ug/mL Kanamycin
12. You can pour the LB agar from the flask into a sterile 500-mL beaker for easier transfer onto the plates. Sterilize the flask mouth by flame. If there's any bubbles formed, you can burst the bubble by passing the flame on the LB agar quickly.
13. Use flame beside to minimize contamination.
14. Open the lid of the top plate and flame the beaker mouth, then pour the LB agar onto the plate until about half-way full.
15. The plates should stand at RT for a day before being bagged and stored. They may be used for experiments later the same day if required.
16. Put the plates inside the bag (Note: Upside Down to avoid drying out!) and store at 4oC.
Reference: http://www.metazoa.com/view-protocol.jsp?ProtocolId=3201&VersionNo=1