Luria Agar (Miller’s LB Agar)

These strains are generally derived from E. coli K12, which are unable to produce vitamin B, so this medium is formulated to enhance the growth of nutritionally demanding microorganisms. This strain of E. coli has been further modified through specific mutation to create an auxotrophic strain that is not capable of growth on nutritionally deficient media.

Tryptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly the B-group. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Bacteriological agar is the solidifying agent.

If desired, aseptically add 10 mL of sterile 20% glucose solution and mix thoroughly for a better growth. Bacteria that contain plasmids tend to grow best in broth that has between 5 and 10 g of salt. Various cofactors may also need to be added to the broth if working with certain types of bacteriophages. For example, bacteriophage lambda requires an excess of magnesium in the broth to properly infect bacteria.

Luria Agar (Miller’s LB Agar) has a different sodium chloride level than other media such as LB Agar (Lennox) (LC-1083) or Luria Agar (Miller’s Modification) (LC-1308). This allows selecting the optimum salt concentration of the medium for a specific strain.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 40 grams of medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 45-50 °C, mix well and dispense into plates.

Instructions for use

1. Carry out the experimental procedure according to appropriate use or purpose.
2. Inoculate and incubate at a temperature of 35 ± 2 °C for 18-24 hours.

• Atlas, R.M., L.C. Parks (1993) Handbook of Microbiological Media. CRC Press, Inc. London.
• The condensed protocols from molecular cloning: a laboratory manual / Joseph Sambrook, David W. Russell.