Endo Agar

LAB 60

Description

This medium was developed in 1914 for the isolation of Salmonella typhi; other media have since proved superior for this purpose, but Endo agar has a role as a coliform medium. It is recommended by the American Public Health Association as a standard medium for the enumeration of coliforms in water and dairy products. In this medium acetaldehyde is produced by coliforms and then fixed by the sulphite to produce a metallic sheen with the basic fuchsin dye. Most enteric Gram negative organisms will grow well, whilst Gram positive organisms are mostly inhibited.

Method for reconstitution

Weigh 41 grams of powder, disperse in 1 litre of deionised water. Add 4ml of a 10% w/v alcoholic solution of basic fuchsins (95% ethyl alcohol). Bring to the boil with frequent swirling to dissolve the solids. Sterilise by autoclaving at 121˚C for 15 minutes. Cool to 47˚C in a water bath before pouring. The precipitate typically associated with this medium should be dispersed by gentle swirling prior to pouring the plates.

This medium is light sensitive and should therefore be stored in the dark, preferably under refrigeration. The medium will become dark red in colour if exposed to light.

Basic Fuchsin is a potential Carcinogen and care should be taken when handling it to avoid inhalation of the powdered dye and contamination of the skin.

Appearance: Pale pink/orange

pH: 7.5 ± 0.2

Minimum Q.C. organisms: E. coli NCIMB 50034

Storage of Prepared Medium: Plates - up to 7 days at 2-8˚C in the dark.

Inoculation: Surface, streaking out for single colonies.

Incubation: 37˚C for 18-48 hours aerobically.

References

Endo, 1914, Centr. Bakt., Abt 1, Orig., 35: 109.

American Public Health Association, 1975. Standard Methods for the Examination of Water and Wastewater, 14th Edn. American Public Health Association, Inc. Washington D.C.

American Public Health Association, 1972. Standard Methods for the Examination of Dairy Products, 13th End., American Public Health Association, Inc., Washington, D.C.