MRS Broth is a medium for the cultivation and enumeration of Lactobacillus spp. It has the same formulation as MRS Agar (Cat. 1043) without the agar as a solidifying agent. It is used when a fluid medium is preferred. It was developed by De Man, Rogosa and Sharpe to provide a medium which allows a good growth of lactobacilli, particularly L. brevis and L. fermenti strains, which have had a poor growth in existing media. This has been achieved by replacing the tomato juice from the Tomato Juice Agar with other nutrients, creating a suitable medium for the growth of lactic acid bacteria, including Lactobacillus, Pediococcus and Leuconostoc. Ammonium citrate at a low pH inhibits most microorganisms, but allows the growth of lactobacilli. Dipotassium phosphate and sodium acetate are buffer agents to maintain a low pH. Tween 80 is an emulsifier. Manganese and magnesium sulfates are sources of ions and sulfate. Bacteriological peptone and beef extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is source of vitamins, particularly the B-group. Dextrose is the fermentable carbon and energy source. The growth of some Lactobacillus strains are inhibited at pH higher than 6,0, so it is necessary to acidify the media to promote the growth. To acidify the media some drops of acetic acid can be added.
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