The filtration technique play role in removing bacteria from fluids when passed through small pore size filters and bacteria are arrested. It enables to pass large volumes of water rapidly under pressure without passing bacteria. The retained nutrients on the surface of the membrane is incubated with suitable liquid nutrients and diffusion occurs in upward direction through the pores thereby inducing the organisms to grow as surface colonies which can be counted. Endo Medium was first developed by Endo to differentiate between lactose-fermenters and non-fermenters. M-Endo Agar, LES is formulated as per McCarthy et al of Lawrence Experimental Station (LES) and is a modification of the original medium for testing coliforms in water using a two-step membrane filter procedure, wherein primary enrichment is used as Lauryl Sulphate Broth. APHA recommended this medium for testing coliforms in drinking and in bottled water. Presumptive coliform bacteria will form red colonies with metallic sheen after an incubation at 35-37?Cfor 24 hours
