Endo Agar Base

It uses fuchsin to differentiate between positive lactose-fermenting and lactose non-fermenting bacteria. Acetaldehyde production by lactose-fermenting organisms such as E. coli produces characteristic red colonies and a red surrounding area, marked by its reaction with sodium sulphite in the presence of fuchsin. Lactose non-fermenters form colorless, transparent colonies.

Peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. Dipotassium phosphate acts as a buffer system. Bacteriological agar is the solidifying agent.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 36 grams of the medium in one liter of distilled water. Add 5 mL of an alcoholic solution at 10% (w/v) of basic fuchsin in 95% ethyl alcohol. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 50 °C, mix well and dispense into plates.

Instructions for use

1. Inoculate on the surface making parallel striae with the loop or swab.
2. Incubate the plates protected from light, at 35 ± 2 °C for 18-24 hours. If after 24 hours it is negative, re-incubate for an additional 24 hours. To confirm the presence of possible coliforms, inoculate the tubes with the Endo Agar Base and incubate at 35 ± 2 °C for 18-24 hours. Examine to determine the production of acid and gas.
3. Reading and interpretation of the results.

Rapid lactose fermenters produce red colonies with a metallic luster. Slow lactose fermenters produce red colonies. Non lactose fermenters produce colorless colonies.

• Endo S. 1904. Über ein Verfahren zum Nachweis der Typhusbacillen.
• A.P.H.A. 1975 Standard methods for the examination of water and wastewater. 14th edition.
• Standard Methods for the Examination of Water and Wastewater (1992).