Letheen Agar with Tween is used for the testing of quaternary ammonium compounds for antimicrobial activity in a laboratory setting. Letheen Agar with Tween 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 while testing germicidal activity. Letheen Agar with Tween is a modification of TGE Agar, with the addition of Lecithin and Tween 80 (Polysorbate 80).

Letheen Agar with Tween is specified for use by the American Society for Testing Materials (ASTM) in Standard Test Method for Preservatives in Water-Containing Cosmetics. Total neutralization of disinfectants is critical. Disinfectant residues can result in a false negative (no-growth) test.

Letheen Agar with Tween has incorporated Tween 80 (Polysorbate 80) into the medium, this is the only difference from Letheen Agar Base.


Formula Liter
Enzymatic Digest of Casein 5 g
Dextrose 1 g
Beef Extract 3 g
Lecithin 1 g
Tween 80 (Polysorbate 80) 7 g
Agar 15 g

Final pH: 7.0 ± 0.2 at 25°C
Formula may be adjusted and/or supplemented as required to meet performance specifications.


  1. Suspend 32 g of the medium 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
7710A Letheen Agar with Tween, 500 g
7710T Letheen Agar with Tween, 5 kg
7710C Letheen Agar with Tween, 10 kg

Reference Material

7710 - Letheen Agar Base with Tween, Product Information Sheet [English] [Portuguese]

For additional information or questions about product SDS documents, please contact Neogen at SDS@neogen.com.


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