MRS agar

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.

It contains sodium acetate, which suppresses the growth of many competing bacteria (although some other Lactobacillales, like Leuconostoc and Pediococcus, may grow).

[1] MRS agar typically contains (w/v):[2] 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.