Letheen Broth Base (no tween) is used with Tween 80 (Polysorbate 80) for the testing of samples containing quaternary ammonium compounds for antimicrobial activity in a laboratory setting. Letheen Broth Base (no 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 neutralising agents for quaternary ammonium compounds in sanitisers. The addition of Lecithin and Polysorbate 80 to Tryptone Glucose Extract (TGE) Agar resulted in a medium that effectively neutralises quaternary ammonium compounds while testing germicidal activity. Letheen Agar is a modification of TGE Agar with the addition of Lecithin and Polysorbate 80.

Letheen Broth Base was developed as a subculture medium for the neutralisation of quaternary ammonium compounds in disinfectant testing. Quisno, Gibby, and Foter discovered that adding Lecithin and Polysorbate 80 to F.D.A. Broth resulted in a medium that neutralised high concentrations of quaternary ammonium salts. The resulting medium, termed "Letheen" (a combination of Lecithin and Tween) was easy to prepare and clear in appearance, aiding to visual inspection for growth. Letheen Broth Base is recommended by the Official Methods of Analysis of the Association of Official Analytical Chemists (AOAC) for use with disinfectants containing cationic surface active materials. Letheen Broth Base is specified for use by the American Society for Testing Materials (ASTM) in Standard Test Method for Preservatives in Water-Containing Cosmetics. Total neutralisation of disinfectants is critical. Disinfectant residues can result in a false negative (no-growth) test.

• Analyte: non-selective
• Platform: dehydrated culture media
• Formula: enzymatic digest of animal tissue 10.0g/L, beef extract 5.0g/L, sodium chloride 5.0g/L, lecithin 0.7g/L
• Grams per litre: 20.70
• Litres per 500g: 24.00