Cat. no. C7410 CRITERION™ m Endo LES Agar 102gm
Cat. no. C7411 CRITERION™ m Endo LES Agar 500gm
Cat. no. C7412 CRITERION™ m Endo LES Agar 2kg
Cat. no. C7413 CRITERION™ m Endo LES Agar 10kg
Cat. no. C7414 CRITERION™ m Endo LES Agar 50kg


Hardy Diagnostics' CRITERION™ m Endo LES Agar is recommended for use in enumerating coliforms in water by the single-step, two-step and delayed incubation membrane filtration methods.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.


CRITERION™ m Endo LES Agar follows the Lawrence Experimental Station (LES) formula developed by McCarthy, et al.(1,2) Through the course of their studies, McCarthy and colleagues employed the use of lauryl sulfate as a primary enrichment broth and followed a two membrane filtration technique as opposed to the most probable number (MPN) method or one-step method. The researchers found that use of a two-step process of enrichment resulted in higher recovery of coliforms and more reliable and precise results.(1,2)

m Endo LES Agar contains deoxycholate and lauryl sulfate, which serve as inhibitory agents against gram-positive microorganisms; lactose, which is a source of fermentable carbohydrate; peptones and yeast extract, which provide necessary growth nutrients; and basic fuchsin acts as the pH indicator.

Microorganisms capable of lactose-fermentation produce acetaldehyde, which reacts with basic fuchsin and sodium sulfite to form a red zone surrounding the colonies. Coliform organisms produce red colonies with a characteristic golden-green metallic sheen. The development of a metallic sheen occurs when the organism produces aldehydes during the rapid fermentation of lactose. If the inoculum is too heavy, the sheen will be suppressed. Bacteria unable to ferment lactose form clear, colorless colonies.

The American Public Health Association specifies using m Endo LES Agar in the standard total coliform membrane filtration procedure for testing drinking and bottled water.(3,4) It is also specified for use in the completed phase of the standard total coliform fermentation technique.(3) The U.S. Environmental Protection Agency specifies using m Endo LES Agar in the total coliform methods for testing water using single-step, two-step and delayed incubation membrane filtration methods.(5,6)


Gram weight per liter: 51.0gm/L
Lactose 9.4gm
Pancreatic Digest of Casein 7.5gm
Peptic Digest of Animal Tissue 7.5gm
Sodium Chloride 3.7gm
Dipotassium Phosphate 3.3gm
Sodium Sulfite 1.6gm
Yeast Extract 1.2gm
Monopotassium Phosphate 1.0gm
Basic Fuchsin 0.8gm
Sodium Deoxycholate 0.1gm
Sodium Lauryl Sulfate 0.05gm
Agar 15.0gm

Final pH 7.2 +/- 0.2 at 25ºC.

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


Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original purple.

Store the prepared media at 2-8ºC.


Warning: Basic Fuchsin is a potential carcinogen and care must be taken to avoid contamination of the skin. If contact occurs, rinse thoroughly with water.


1. Suspend 51.0gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Add 20ml of ethanol (95%, not denatured).

3. Heat to 97.5 - 98.5ºC. Do not allow to boil. Do not autoclave.

4. Cool to 50-55ºC. and dispense approximately 5-7ml into sterile 60mm petri dishes.

5. Protect from light. This product is extremely light sensitive.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G28.


Variations in degree of metallic sheen development may be observed among coliform strains.(3)


Standard microbiological supplies and equipment such as autoclaves incinerators, and incubators, etc., are not provided.


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli**
ATCC ® 25922
MF 24hr 35°C Aerobic Growth; red to red-black colonies with a metallic sheen
Salmonella enterica
ATCC ® 14028
MF 24hr 35°C Aerobic Growth; colorless colonies
Staphylococcus aureus**
ATCC ® 25923
B 24hr 35°C Aerobic Inhibited

** Recommended QC strains for User Quality Control according to the CLSI document M22 when applicable.

User Quality Control


CRITERION™ m Endo LES Agar powder should appear homogeneous, free-flowing, and purple in color. The prepared media should appear opalescent with a slight precipitate throughout, and light rose in color.


1. McCarthy, J.A., et al. 1961. Water Sewage Works; 108:238-243.

2. McCarthy, J.A., et al. 1958. AJPH; 48:16-28.

3. Standard Methods for the Examination of Water and Wastewater, 19th ed. 1995. American Public Health Association, Washington, D.C.

4. Cowman, S. and R. Kelsey. 1992. Compendium of Methods for the Microbiological Examination of Foods, 3rd ed. American Public Health Association, Washington, D.C.

5. Bordner, R. and J. Winter. 1978. Microbiological Methods for Monitoring the Environment, Water and Wastes, EPA-600/8-78-017. Environmental Monitoring and Support Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH.

6. Environmental Protection Agency. Manual for the Certification of Laboratories Analyzing Drinking Water, EPA-814B-92-002. Office of Ground Water and Technical Support Division, U.S. Environmental Protection Agency, Cincinnati, OH, 1992.

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