Letheen Broth

Intended Use

Letheen Broth is used for determining the phenol coefficient of cationic surface-active materials.

Summary and Explanation

The value of a highly nutritional solid medium containing neutralizing agents for quaternary ammonium compounds in sanitizers was described by Weber and Black¹ in 1948. The addition of lecithin and polysorbate 80 (Tween™* 80) to Tryptone Glucose Extract (TGE) agar resulted in a medium that effectively neutralizes quaternary ammonium compounds in the testing of germicidal activity. Letheen Agar is a modification of TGE agar with the addition of lecithin and polysorbate 80.
Letheen Broth was developed as a subculture medium for the neutralization of quaternary ammonium compounds in disinfectant testing. Quisno, Gibby and Foter² found that the addition of lecithin and polysorbate 80 to F.D.A. Broth resulted in a medium that neutralized 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, which aided in visual inspection for growth. Letheen Broth is recommended in the Official Methods of Analysis of AOAC International³ for use with disinfectants containing cationic surface active materials.
Letheen Agar and Letheen Broth are specified for use by the American Society for Testing and Materials (ASTM) in the Standard Test Method for Preservatives in Water-Containing Cosmetics.⁴
*Tween is a trademark of ICI Americas, Inc.

Principles of the Procedure

Letheen Broth contains peptone and beef extract which provide the carbon and nitrogen sources necessary for growth. Lecithin and polysorbate 80 are added as surface active disinfectant neutralizing agents.^2,5,6 Sodium chloride is included to maintain osmotic balance.

User Quality Control

Identity Specifications
Letheen Broth
Dehydrated Appearance: Tan, appears moist, with a tendency to clump.
Solution:                        2.57% solution, soluble in purified water upon
                                     boiling. Solution is light amber, clear to slightly
                                     opalescent (opalescent when hot). May have a
                                     very slight precipitate.
Prepared Appearance:     Light to medium amber, clear to slightly opalescent,
                                     may have a slight precipitate.
Reaction of 2.57%
Solution at 25°C:            pH 7.0 ± 0.2
Cultural Response
Letheen Broth
Prepare the medium per label directions. Inoculate and incubate at 35 ± 2°C for 40- 48 hours.

Formula

Letheen Broth
Approximate Formula* Per Liter
Beef Extract.................................................................. 5.0 g
Proteose Peptone No. 3................................................ 10.0 g
Polysorbate 80 ............................................................. 5.0 g
Lecithin......................................................................... 0.7 g
Sodium Chloride............................................................ 5.0 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend the powder in 1 L of purified water:
Letheen Broth – 25.7 g. Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes.
4. Test samples of the finished product for performance using stable, typical control cultures.
NOTE: The dehydrated Letheen Agar has a characteristic “brown sugar” appearance and may seem moist. This does not indicate deterioration.

Procedure

Letheen Agar and Letheen Broth are used in a variety of procedures. Consult appropriate references for further information.^3,4

Expected Results

Refer to appropriate references and procedures for results.^3,4

*Store at 2-8° C.

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