Description
The formula for MRS was developed by deMan, Rogosa and Sharpe, based on earlier work by Rogosa to provide an alternative culture medium to Tomato Juice Agar which is an inconsistent product difficult to standardise batch to batch, and also because MRS medium is more successful in the cultivation of the slower growing Lactobacilli for example L. fermentum and L. brevis.
Other lactic acid fermenting genera: Streptococcus, Pediococcus and Leuconostoc with similar properties to Lactobacillus in terms of being oxidase and catalase negative and Gram stain positive are also supported.
Colony size on agar is enhanced by micro-aerophilic conditions but layer plates may be used for aerobic cultivation.
Most Lactobacilli are slow growing and require 2-4 days incubation.
Sodium Acetate and Ammonium Citrate render the medium more selective by inhibiting the growth of Gram negative, moulds and unwanted oral flora. Lowering of pH allows Lactobacilli to grow at the expense of Streptococci although Enterococci may grow poorly
