Cat. no. C7640 CRITERION™ Modified Letheen Broth 85.6gm
Cat. no. C7641 CRITERION™ Modified Letheen Broth 500gm
Cat. no. C7642 CRITERION™ Modified Letheen Broth 2kg
Cat. no. C7643 CRITERION™ Modified Letheen Broth 10kg
Cat. no. C7644 CRITERION™ Modified Letheen Broth 50kg


Hardy Diagnostics CRITERION™ Modified Letheen Broth is for use in microbial recovery from personal care products and for the neutralization of quaternary ammonium compounds in the testing of germicidal activity.

Dehydrated culture media is a raw material not intended for use in the diagnosis of human disease. For implementation, this product requires additional processing and supplementation of ingredients before use.


Quaternary ammonium compounds are molecules which contain a nitrogen atom bonded to four other atoms. Most quaternary ammonium compounds are organic compounds that have biological activity. These compounds often work well as disinfectants, offering bactericidal and bacteriostatic effects. Modified Letheen Broth is used in the AOAC procedure for determining the effect of these bactericidal compounds.(1)

Modified Letheen Broth is formulated as described in the 7th edition of the U.S. FDA Bacteriological Analytical Manual and is recommended by the FDA for use in the microbiological testing of cosmetics.(1) The medium contains beef extract and peptone which provide a nutrient rich medium of vitamins, amino acids and nitrogen to support the growth of a variety of microorganisms. Yeast extract provides vitamins and co-factors which serve as additional sources of nitrogen and carbon required for bacterial growth. Modified Letheen Broth also contains lecithin and Tween® 80. Quaternary ammonia compounds are neutralized by lecithin while phenolic disinfectants and hexachlorophene are neutralized by Tween® 80. Together, lecithin and Tween® 80 neutralize ethanol.(1)


Gram weight per liter: 42.8gm/L
Letheen Broth 25.7gm
Proteose Peptone No. 3 10.0gm
Casein Peptone 5.0gm
Yeast Extract 2.0gm
Sodium Bisulfite 0.1gm

Final pH 7.2 +/- 0.2 at 25ºC.

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


Store the sealed bottle(s) that contain dehydrated culture medium at 2-8ºC. Dehydrated culture medium is very hygroscopic and will clump when exposed to moisture and air. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. Dehydrated culture media should be discarded if it is not moist and lumpy or if the color has changed from its original beige.

Store the prepared culture media at 2-8ºC and do not remove the container desiccant, if applicable.



1. Suspend 42.8gm of the dehydrated culture media in 1 liter of distilled or deionized water. Stir to mix thoroughly.

2. Heat as necessary to dissolve completely.

3. Dispense into appropriate container.

4. Sterilize in the autoclave at 121ºC. for 15 minutes.

Note: The shelf life of in-house prepared media from dehydrated culture media is dependent upon preparation methods, container quality, equipment, storage conditions, and batch testing criteria and must be validated by the end user.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. K293.


Accurate counting may be difficult with molds or spreading colonies.

Rare, fastidious microorganisms may not grow on selective media formulations.


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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Staphylococcus aureus
ATCC ® 25923
A 18-48hr 35°C Aerobic Growth; turbidity
Staphylococcus aureus
ATCC ® 6538
A 18-48hr 35°C Aerobic Growth; turbidity

User Quality Control

Physical Appearance

CRITERION™ Modified Letheen Broth powder should appear moist, lumpy, and beige in color. The prepared media should appear slightly opalescent, may have a slight fine precipitate, and medium-dark amber color.


1. Tomlinson, L. (ed.). 1992. FDA Bacteriological Analytical Manual, 7th ed. AOAC International, Arlington, VA.

2. Hitchins, A.D., T.T. Tran, and J.E. McCarron. 1995. FDA Bacteriological Analytical Manual, 8th ed. AOAC International, Gaithersburg, MD.

3. Marshall, R.T., (ed.). 1992. Standard Methods for the Examination of Dairy Products, 16th ed. APHA, Washington, D.C.

4. Vanderzant, C. and D.F. Splittstoesser, (ed.). 1992. Compendium of Methods for the Microbiological Examination of Foods, 3rd ed. APHA, Washington, D.C.

5. Greenberg, A.E., et al. (ed.). 1992. Standard Methods for the Examination of Water and Wastewater, 18th ed. APHA, Washington, D.C.

6. U.S. Pharmacopeia, 22nd rev. 1990. U.S. Pharmacopeial Convention, Rockville, MD.

7. MacFaddin, J.F. 1985. Media for Isolation, Cultivation, Identification, Maintenance of Bacteria, Vol. I. Williams & Wilkins, Baltimore, MD.

8. Quality Assurance for Commercially Prepared Microbiological Culture Media, M22. Clinical and Laboratory Standards Institute (CLSI - formerly NCCLS), Wayne, PA.

9. Helrich, Kenneth, (ed.). 1990. Official Methods of Analysis, 15th ed. AOAC, Arlington, VA.

ATCC is a registered trademark of the American Type Culture Collection.

Tween is a registered trademark of ICI Americas, Inc.