Letheen Agar Base, Modified

Letheen Agar Base, Modified is used with Tween 80 (Polysorbate 80) for the isolation of microorganisms from cosmetics in a laboratory setting. Letheen Agar Base, Modified is not intended for use in the diagnosis of disease or other conditions in humans.

In 1948, Weber and Black described the value of a highly nutritional solid medium containing neutralizing agents for quaternary ammonium compounds in sanitizers. The addition of Lecithin and Tween 80 (Polysorbate 80) to Tryptone Glucose Extract (TGE) Agar resulted in a medium that effectively neutralizes quaternary ammonium compounds in testing of germicidal activity. Total neutralization of disinfectants is critical. Disinfectant residues can result in a false negative (no-growth) test.

Letheen Agar Base, Modified is based on the formula described in FDA Bacteriological Analytical Manual, and a modification of Letheen Agar Base. Letheen Agar Base, Modified is recommended by the FDA for use in the microbiological testing of cosmetics.


Formula Liter
Letheen Agar Base 25 g
Enzymatic Digest of Casein 10 g
Enzymatic Digest of Animal Tissue 10 g
Yeast Extract 2 g
Sodium Chloride 5 g
Sodium Bisulfite 0.1 g

Final pH: 7.2 ± 0.2 at 25°C
Formula may be adjusted and/or supplemented as required to meet performance specifications.

Supplement / Liter

Tween 80 (Polysorbate 80), 7 mL
Note: Equivalence for Tween 80 in grams to mL is @ 1:1


  1. Suspend 52.1 g of the medium and 7 mL of Tween 80 (Polysorbate 80) in one liter of purified water.
  2. Heat with frequent agitation and boil for one minute to completely dissolve the medium.
  3. Autoclave at 121°C for 15 minutes.

Order Details

Product # Product Description
7495A Letheen Agar Base, Modified, 500 g
7495T Letheen Agar Base, Modified, 5 kg