LB Broth (Lennox)

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. Cultivation in LB Broth allows cells with an insert plasmid to start expressing the genes on the transformed plasmid, including the antibiotic resistance gene. If transformed E. coli are plated directly onto selective agar media (LB Agar containing antibiotic), fewer transformed colonies will appear per mL plated. Growing the transformed cells in LB Broth will increase the number of transformed cells per mL.

LB Broth (Lennox) contains ten times the sodium chloride level of Luria Broth (Miller’s Modification) (LC-1266) and half of the level found in Luria Broth (Miller’s LB Broth) (LC-1551). This allows selecting the optimal salt concentration medium for a specific strain.

Tryptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is the source of vitamins, particularly of the B-group. Sodium chloride supplies essential electrolytes for transport and osmotic balance. This medium consists of the same ingredients as LB Agar (Lennox) without bacteriological agar. If desired, antibiotics can also be added.

Preparation

Suspend 20 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

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.
• Lennox. (1955). Virology 1:190.
• Sambrook, Fritsch and Maniatis. (1989). Molecular cloning: a laboratory manual, 2nd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.