De Man–Rogosa–Sharpe agar, often abbreviated to MRS, is a selective culture medium designed to favour the luxuriant growth of Lactobacilli for lab study. Developed in 1960, this medium was named for its inventors, , , and M Elisabeth Sharpe. It contains sodium acetate, which suppresses the growth of many competing bacteria (although some other Lactobacillales, like Leuconostoc and Pediococcus, may grow). This medium has a clear brown colour.EMD Chemicals, MRS Agar , 2002.
Typical composition MRS agar typically contains (w/v):
1.0% peptone 1.0% beef extract 0.4% yeast extract 2.0% glucose 0.5% sodium acetate trihydrate 0.1% polysorbate 80 (also known as Tween 80) 0.2% dipotassium hydrogen phosphate 0.2% triammonium citrate 0.02% magnesium sulfate heptahydrate 0.005% manganese sulfate tetrahydrate 1.0% agar pH adjusted to 6.2 at 25 °C
The yeast/meat extracts and peptone provide sources of carbon, nitrogen, and vitamins for general bacterial growth. The yeast extract also contains vitamins and amino acids 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.
See also MacConkey agar (culture medium designed to grow Gram-negative bacteria and differentiate them for lactose fermentation).
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