Liofilchem™ LETHEEN Agar Base

Liofilchem™ Letheen Agar Base is a dehydrated basal culture medium specifically formulated for the evaluation of bactericidal activity of quaternary ammonium disinfectants and other sanitizer compounds.

This medium is widely used in disinfectant efficacy testing, environmental monitoring, cosmetic microbiology, and preservative challenge studies, where neutralization of residual antimicrobial agents is essential for accurate microbial recovery.

When supplemented with lecithin and Tween 80, Letheen Agar Base becomes an effective neutralizing medium that supports the growth of microorganisms while inhibiting the carry-over effects of quaternary ammonium compounds.

The American Society for Testing and Materials (ASTM) recommends Letheen Agar in the Standard Test Method for Preservatives in Water-Containing Cosmetics, highlighting its importance in quality control and regulatory microbiology.

Intended Use

Letheen Agar Base is intended for:

• Neutralization and recovery testing of microorganisms exposed to disinfectants
• Evaluation of bactericidal activity of quaternary ammonium sanitizers
• Preservative efficacy testing in cosmetics and personal care products
• Environmental surface monitoring in hygienic manufacturing settings
• Microbiological quality control in pharmaceutical and industrial laboratories

Principle of the Medium

Letheen Agar Base provides a nutritionally supportive environment for bacterial growth while allowing neutralization of disinfectant residues through supplementation.

Key Components and Functions

• Beef Extract
  Supplies vitamins, minerals, and essential growth factors.
• Tryptone
  Provides nitrogen, carbon, sulfur, and amino acids necessary for microbial growth.
• Glucose
  Acts as an energy source to enhance organism recovery.
• Agar
  Solidifying agent for plate culture applications.
• Neutralizing Agents (Added Supplements)
  • Lecithin neutralizes quaternary ammonium compounds
  • Tween 80 (polysorbate 80) neutralizes phenolic disinfectants and enhances neutralization activity

These neutralizers prevent false-negative results by ensuring that disinfectant residues do not continue inhibiting microbial growth after sampling.

Typical Formula

Preparation Instructions

1. Suspend 24.0 g of powder in 1 liter of distilled or deionized water.
2. Add:
   • 10 mL Letheen Supplement (Ref. 80008)
   • 7 mL Tween 80 Supplement (Code 80031)
3. Heat to boiling with shaking until completely dissolved.
4. Sterilize by autoclaving at 121°C for 15 minutes.
5. Dispense into sterile Petri dishes or final containers.

Applications & Technique

Letheen Agar Base is used in a variety of microbiological procedures, including:

• Disinfectant and sanitizer neutralization studies
• Cosmetic preservative testing (ASTM E640)
• Environmental monitoring of sanitized surfaces
• Recovery of stressed bacteria following chemical exposure

Users should consult relevant standards and laboratory protocols for specific test methods.

Appearance

Quality Control Performance

Sterility controls are performed under aerobic conditions at 25°C and 36°C.

Storage & Shelf Life

• Store dehydrated powder at 10–30°C in a dry environment, tightly closed.
• Prepared media should be stored at 2–8°C.

Shelf Life:

• Dehydrated medium: 4 years

Packaging Information

Regulatory & Reference Standards

• ASTM Standard Test Method for preservatives in water-containing cosmetics (E640)
• AOAC Official Methods of Analysis
• Published disinfectant neutralization studies (Weber & Black, 1948)

Liofilchem™ Letheen Agar Base is a trusted basal medium for neutralizing quaternary ammonium disinfectants and supporting microbial recovery in disinfectant testing, cosmetics quality control, and environmental monitoring. When properly supplemented with lecithin and Tween 80, it ensures accurate evaluation of bactericidal performance by eliminating residual sanitizer interference.