For primary isolation of coliforms from large samples like water. It is recommended by BIS committee under specification IS:5887 (Part I) 1976, reaffirmed 2005. MacCONKEY BROTH W/ NEUTRAL RED is used for selective enrichment and enumeration of coliforms. The medium contains Peptic digest of animal tissue which provides the nitrogeneous and other essential growth compounds. Sodium chloride maintains the osmotic balance of the cells. The selective action ofthese media is attributed to the presence of bile salts, which are inhibitory to most species of gram-positive bacteria.Gram-negative bacteria usually grow well on these media and are differentiated bytheir ability to ferment lactose. Thecolour change of the medium shown by lactose-fermenters is due to production of acid from lactose and a subsequentcolour change of the indicator dye when the pH of the media falls below 6.8. Bile salts which inhibits the growth of gram positive microorganisms. The medium turns pink in case of lactosefermenters and yellow in case of non-lactose-fermenters, due to neutral red. Organism producing gas can be observed in preparation with Durham tubes. Inoculate the test tubes with specimen, incubation at 43 ± 1ºC for 24-48 hours .The most probable number of coliforms per 100ml water is obtained from McGrady's tables. Confirmation of positive results is carried out by subculture onto solid media such as Endo Agar or MacConkey Agar (without salt).