m-Endo Agar (LES) (ISO9308-1)

Product information

m-Endo Agar is used for the enumeration of coliforms in water by the membrane filtration method.

Product Summary and Explanation
The coliform group, especially Escherichia coli, are used as indicators of fecal pollution in water, for assessing the effectiveness of water treatment and disinfection, and for monitoring water quality. m-Endo Agar is prepared according to the formula of McCarthy, Delaney, and Grasso,1 and used in testing water for coliforms by a two-step membrane filtration procedure. Lauryl Tryptose Broth is used as the preliminary enrichment, resulting in higher coliform counts.

The APHA recommends m-Endo Agar in standard total coliform membrane filtration procedure for testing water, wastewater, and foods.2,3 The US EPA specifies using m-Endo Agar in the total coliform methods for testing water.4,5 m-Endo Agar is also known as LES (Lawrence Experimental Station) Endo Agar.1

Principles of the Procedure
Tryptose, Enzymatic Digest of Casein, and Enzymatic Digest of Animal Tissue, provide nitrogen, carbon, and minerals in m-Endo Agar. Yeast Extract is a source of vitamins and trace elements to stimulate bacterial growth. Potassium Phosphates are the buffering agents. Sodium Chloride maintains the osmotic balance. Lactose serves as a carbohydrate source. Sodium Lauryl Sulfate and Sodium Deoxycholate are selective agents used to inhibit of Gram-positive bacteria. Basic Fuchsin is a pH indicator. Sodium Sulfite is added to decolorize the Basic Fuchsin solution. Ethanol aids is the homogeneity of the solution and as a selective agent. Agar is the solidifying agent.

Lactose positive colonies exhibit a red color caused by the aldehyde reaction with the Sodium Sulfite and Basic Fuchsin. The development of a metallic sheen occurs when the organism produces aldehydes with the fermentation of Lactose. Lactose non-fermenting bacteria form clear, colorless colonies.

Formula / Liter Supplement
Lactose........................................................9.4 g Non-denatured Ethanol, 20 mL
Tryptose.......................................................7.5 g
Enzymatic Digest of Casein...............................3.7 g
Enzymatic Digest of Animal Tissue.....................3.7 g
Sodium Chloride.............................................3.7 g
Potassium Phosphate, dibasic...........................3.3 g
Sodium Sulfite...............................................1.6 g
Yeast Extract................................................1.2 g
Potassium Phosphate, monobasic.....................1.0 g
Basic Fuchsin.................................................0.8 g
Sodium Deoxycholate.....................................0.1 g
Sodium Lauryl Sulfate...................................0.05 g
Agar.............................................................15 g
Final pH: 7.2 ± 0.2 at 25°C