de Man, Rogosa & Sharpe (MRS) Agar
M.R.S. Agar is intended for the cultivation and enumeration of Lactobacillus spp from a variety of sources and can be used as an alternative to Orange Serum Agar for that purpose. Magnesium Sulphate, Manganese Sulphate, Sodium Acetate and Tween are included as growth supplements. The medium can be made more specific for lactobacilli generally by lowering the pH to between 5.0 and 5.5. This has the effect of inhibiting most streptococci that may otherwise grow on the medium and can be readily confused with lactobacilli.