M-Endo Agar

Principle

• M-Endo agar is composed of tryptone, peptone, tryptose, yeast extract, lactose, Dipotassium phosphate monobasic and dibasic, sodium chloride, sodium deoxycholate, sodium lauryl sulfate, sodium sulfite, basic fuchsin, and agar. tryptone, peptone, tryptose, and yeast extract, is the source of nitrogenous substances and other essential growth nutrients for the organisms.
• Lactose is a carbon source and phosphate acts as a buffering agent. Sodium chloride makes osmatic equilibrium. Sodium deoxycholate, Sodium sulfite, and basic fuchsin is a selective agent that inhibits the growth of gram-positive bacteria.
• Coliforms give pink color colonies due to lactose fermentation while lactose non-fermenters produce colourless colonies.  
• In the first step of enrichment, the cotton absorbent pad is impregnated with Lauryl Sulphate Broth. Aseptically transfer the water sample through the membrane filter, placed it on it, and incubated without inverting for 2.0 hours at 35°C in a humid atmosphere. After incubation, the membrane filter is aseptically transferred to the M-Endo Agar plate and incubated at 35°C for 24 hours.
• Otherwise, the membrane filter pad can be placed inside the lid of the Petri plate of M-Endo Agar and then soaked with 2.00 ml Lauryl Sulphate Broth and incubated for 1 - 1½ hours at 35°C.
• In the second step, the prepared membrane filter is kept directly on the agar surface and incubated as described above. Presumptive coliforms produce golden green colonies with metallic sheen within 24 hours of incubation.

Use: Recommended for enumeration of coliforms in water using a two-step membrane filtration technique.