MODIFIED LETHEEN AGAR

Cat. no. G221 Modified Letheen Agar, 15x100mm Plate, 18ml 10 plates/bag
Cat. no. W55 Modified Letheen Agar with Tween® 80, 1.5%, 15x100mm Plate, 28ml 10 plates/bag

INTENDED USE

Hardy Diagnostics Modified Letheen Agar is used to determine the antimicrobial activity of quaternary ammonium compounds and in the microbial enumeration of cosmetics.

This product is not intended to be used for the diagnosis of human disease.

SUMMARY

Quaternary ammonium compounds are molecules which contain a nitrogen atom bonded to four other atoms. Most quaternary ammonium compounds are organic compounds and have biological activity. These compounds often work well as disinfectants, offering bactericidal and bacteriostatic effects. Quaternary ammonium compounds are neutralized by lecithin, while phenolic disinfectants, formalin, and hexacholorphene are neutralized by Tween® 80. Together, lecithin and Tween® 80 neutralize ethanol.

Modified Letheen Agar is formulated as described by the U.S. FDA Bacteriological Analytical Manual.(1) Modified Letheen Agar is recommended by the FDA for use in the microbiological testing of cosmetics.(1,2) The medium contains beef extract and peptone to provide a nutrient rich medium supporting the growth of a wide variety of microorganisms. Modified Letheen Agar contains an elevated tryptone level to promote growth. Yeast extract provides vitamins and co-factors, and also serves as an additional source of nitrogen and carbon. Sodium chloride helps maintain osmotic balance. Modified Letheen Agar with Tween® 80, 1.5% contains additional Tween® 80 to further neutralize and reduce the surface tension of sampled materials.

FORMULA

Ingredients per liter of deionized water:*

Letheen Agar 32.0gm
Proteose Peptone No. 3 10.0gm
Tryptone 5.0gm
Sodium Chloride 5.0gm
Yeast Extract 2.0gm
Sodium Bisulfite 0.1gm
Agar 5.0gm

In addition, Modified Letheen Agar with Tween® 80, 1.5% contains:

Tween® 80 8.0gm

Final pH 7.2 +/- 0.2 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

PRECAUTIONS

PROCEDURE

Consult listed references and regulatory guidelines for best practices. (1-6)

1. Prepare and dilute samples in Modified Letheen Broth in accordance with established guidelines.

2. Using the spread plate technique, inoculate in duplicate 0.1ml of the diluted samples onto Modified Letheen Agar, Potato Dextrose Agar (or Malt Extract Agar) containing chlortetracycline, Baird-Parker Agar (or Vogel-Johnson Agar, optional), Anaerobic Agar, and a second set of Modified Letheen Agar plates.

3. Incubate one set of Modified Letheen Agar plates at 30 +/- 2ºC. for 48 hours and the other set at 35 +/- 2ºC. for 2-4 days. Incubate the Potato Dextrose Agar (or Malt Extract Agar) plates at 30 +/- 2ºC. for 7 days, and the Baird-Parker Agar (or Vogel-Johnson Agar) plates, if inoculated, at 35 +/- 2ºC. for 48 hours.

4. Incubate the diluted samples from step 1 at 35 +/- 2.0ºC. for 7 days. Subculture enriched samples onto Modified Letheen Agar only if there is no growth on the primary Modified Letheen Agar plates.

INTERPRETATION OF RESULTS

See listed references for the interpretation of growth using Modified Letheen Agar. (1-6)

LIMITATIONS

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as loops, swabs, applicator sticks, other culture media, incinerators, and incubators, etc., as well as serological and biochemical reagents, are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Modified Letheen Agar (Cat. no. G221):**
Staphylococcus aureus
ATCC® 25923
J 24hr 35°C Aerobic Growth
Escherichia coli
ATCC® 25922
J 24hr 35°C Aerobic Growth
Modified Letheen Agar with Tween® 80, 1.5% (Cat. no. W55):**
Candida albicans
ATCC® 10231
J 1-3days 35°C Aerobic Growth
Staphylococcus aureus
ATCC® 25923
J 1-3days 35°C Aerobic Growth
Escherichia coli
ATCC® 25922
J 1-3days 35°C Aerobic Growth
Pseudomonas aeruginosa
ATCC® 9027
J 1-3days 35°C Aerobic Growth

** Tested in accordance with USP. (6)

USER QUALITY CONTROL

Physical Appearance

Modified Letheen Agar and Modified Letheen Agar with Tween® 80, 1.5% should appear clear, and light amber in color.

REFERENCES

1. U.S. Food and Drug Administration. Bacteriological Analytical Manual. AOAC, Arlington, VA.
http://www.fda.gov/Food/FoodScienceResearch/LaboratoryMethods/ucm2006949.htm.

2. Orth, D.S. 1993. Handbook of cosmetic microbiology. Marcel Dekker, Inc. New York, NY.

3. American Public Health Association. Standard Methods for the Examination of Dairy Products. APHA, Washington, D.C.

4. American Public Health Association Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods. APHA, Washington, D.C.

5. American Public Health Association. Standard Methods for the Examination of Water and Wastewater. APHA, Washington, D.C.

6. United States Pharmacopoeia and National Formulary (USP-NF). Rockville, MD: United States Pharmacopeial Convention.


ATCC is a registered trademark of the American Type Culture Collection.
Tween is a registered trademark of ICI Americas, Inc.

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