LB Agar (Lennox L Agar), powder (Invitrogen™)

LB Agar (Lennox L agar) is a solid agar media powder recommended for the general maintenance and growth of E. coli strains. As E. coli is unable to digest agar but can absorb nutrition from the LB medium, single colonies can be easily isolated and selected. With addition of a selective antibiotic, only transformed E. coli with resistance to that antibiotic can grow. The Lennox formulation has lower levels of salts than Miller and so is preferred when using salt-sensitive antibiotics such as Zeocin, tetracycline, or chloramphenicol.

Lennox broth is a popular, rich medium used to cultivate bacteria and to perform coliphage plaque assays. The original formulation was published in 1951 by Guiseppe Bertani in his study of phage plaque formation and named as Lysogeny broth. It is also known as Lennox broth and Luria-Bertani broth.

Solid culture media have been a major turning point for bacteriology, introduced by Robert Koch in 1881 by adding liquid cultures in gelatin (later replaced by agar derived from seaweed as per Walter Hesse's discovery). This allowed plated bacteria to form visible colonies on a solid and smooth surface. Koch’s assistant, Julius Petri, designed a shallow dish with a lid where medium could be poured, cooled to solidity, and protected from contamination.

Widely used LB medium formulations differ in salt concentration:
• Miller: 10 g/L NaCl
• Lennox: 5 g/L NaCl
• Luria: 0.5 g/L NaCl

LB Agar (Lennox L agar) formulation and preparation
Formulation per liter: 10 g SELECT Peptone 140, 5 g SELECT Yeast Extract, 5 g NaCl, and 12 g SELECT Agar.
To prepare 1 L of LB Agar medium (1.2% final agar concentration), weigh 37 g of powder and add distilled water to 1 L. Adjust the pH value to 7.0 with 5 N NaOH and sterilize by autoclaving for 25 minutes at 121°C.

Primary applications
• Select using antibiotic transformed E. coli colony with constructed DNA plasmid
• Streaking and isolating bacteria cells on LB agar plate
• Blue-white screening using X-Gal or Bluo-gal and IPTG LB agar plates

Find the media format that you need
We offer other ready-to-use media formulations, such as LB (Lennox), Terrific Broth or S.O.C recovery medium.
Explore other media formats for bacterial growth.
Explore our media additives: X-Gal, Bluo-gal, IPTG.