Letheen Broth Base, AOAC (Powder)
Letheen Broth Base is used with Polysorbate 80 for the testing of quaternary ammonium compounds for antimicrobial acitivity. Polysorbate 80 is not supplied. In 1948, Weber and Black described the value of a highly nutitional solid medium containing neutralizing agents for quaternary ammonium compounds for sanitizers. The addition of Lecithin and Polysorbate 80 to Tryptone Gluse Extract (TGE) Agar resulted in a medium that effectively neutralizes quaternary ammonium compounds while testing germicidal activity. Letheen Agar is a modification of TGE Agar with the addition of Lecithin and Polysorbate 80.
Letheen Base was developed as a subculture medium for the neutralization of quaternary ammonium compounds in disinfectant testing. Quisno, Gibby and Foter discovered that adding lecithin and Polysorbate 80 to FDA Broth results in a medium that neutralized high concentrations of quaternary ammonium salts. he 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 Association of Official Analytical Chemists (AOAC) for use with disinfectants containing cationic surface materials.
Letheen Broth Base is specified for use by the American Society for Testing Materials (ASTM) in Standard Test Method for Presernatives in Water-Containg Cosmetivcs. Total neutralization of disinfectants is critical. Disinfectant residues can results in false negative (no growth) tests.
Principles of the Procedure
Enzymatic digest of Animal Tissue and Beef Extract provide nitrogen, carbon, vitamins, and minerals in Letheen Broth Base. Sodium Chloride maintains the osmotic balance. Lecithin neutralizes quaternary ammonium compouNone Detectedsand Polysorbate 80 neutralizes phenols, hexachloraphene, formalin, and with Lecithin, ethanol.
Appearance
Beige, homogeneous, free flowing powder
Solubility
Gold to amber, clear, complete
Directions per Liter
Dissolve 20.7 grams and 5g Polysorbate 80 in 800-900ml of ddH2O stirring gently with heating until completely solubilized. Adjust pH of the medium to the desired level. Add additional water to bring the solution to 1L. Heat with frequent agitation and boil for one minute to completely dissolve the medium. Dispense into appropriate containers, loosen caps and autoclave for 15 minutes at 121ºC (15psi).
Storage and Stability
Store powdered media at RT. Stable for 12 months after receipt. Opened bottles should be capped tightly and kept in a dark, low humidity environment. Prepared media should be kept at 4°C and used within a short period of time.
| Beef Extract | 5 |
| Lecithin | 0.7 |
| Enzymatic Digest of Animal Tissue | 10 |
| Sodium Chloride | 5 |
