MRS Medium, named for its inventors De Man, Rogosa and Sharpe is a selective culture medium designed to favour the luxuriant growth of Lactobacilli in bacteriological cell cultures.
Although MRS medium is selective for lactobacilli but some growth of leuconostocs and pediococci may occur. One of the constituents of MRS is sodium acetate, which suppresses the growth of many competing bacteria.
Yeast extract and meat extract present in MRS medium provide sources of carbon, nitrogen, and vitamins for general bacterial growth. The yeast extract also contains vitamins and amino acids specifically required by Lactobacilli.
Polysorbate 80 is a surfactant which assists in nutrient uptake by Lactobacilli.
Magnesium sulfate and manganese sulfate provide cations used in metabolism.