Lactobacilli MRS Agar is used for the cultivation of lactobacilli and is not intended for use in the diagnosis of disease or other conditions in humans.
MRS Agar is a medium for the cultivation and enumeration of Lactobacillus spp. Originally developed in 1960 by de Man, Rogosa & Sharpe, the medium is suitable for most lactic acid bacteria and is intended as a substitute for Tomato Juice Agar. When acidified to pH 5.4 MRS Agar can be used to enumerate Lactobacillus bulgaricus in yogurts.
Nutrition is provided by a mixture of carefully selected peptones, glucose, beef & yeast extracts while Tween® 80, magnesium and manganese sulfates act as growth stimulants. Selectivity against streptococci & molds is provided by ammonium citrate and sodium acetate. Used at low pH, ammonium citrate allows growth of lactobacilli while inhibiting a number of other microorganism groups. Occasionally, sterilization of this medium at 121°C for 15 minutes, in some autoclaves, may cause the pH to fall outside of the specified pH limits 6.4 +/- 0.2. In these rare cases, adjustment of the medium using acetic acid or sodium hydroxide is recommended.
