Selective medium & Differential medium

A selective medium is one that allows the proliferation of some organisms while repressing the thriving of others. Selection is done through (1) regulation of medium composition, (2)modification of atmospheric or (3) alteration of incubation temperature. A differential medium, however, does not inhibit the proliferation of organisms and will cause some colonies to grow unusually from other existing organisms. Current media includes both selective and differential ingredients. One example of such preparation is Bacto-Brilliant Green gar, which happens to be a highly precise preparation used for the separation of Salmonella species other than S. Typhi, the agent (responsible for the onset of Typhoid Fever) is commonly found in feces or other specimens thought to encompass these organisms. The brilliant green dye represses the proliferation of other bacteria. In its composition, lactose and sucrose acts as the main source for enzymatic action. On normalcy, Salmonella appears as pink-white opaque colonies ringed with brilliant red zones. Easily differentiated, organisms that have same capacity as Salmonella to proliferate on the medium are demarcated by appearance of yellow-green colonies ringed with intense yellow-green areas.