MRS Agar is a medium for the enumeration of mesophilic lactic acid bacteria according to ISO 15214:1998, and is not intended for use in the diagnosis of disease or other conditions in humans. MRS Agar was originally developed in 1960 by de Man, Rogosa & Sharpe for the cultivation and enumeration of Lactobacillus spp. from various sources and is intended as a substitute for Tomato Juice Agar. This original formulation has been adapted and adjusted to pH 5.7 according to ISO 15214:1998.

Nutrition is provided by enzymatic digest of casein, glucose, meat and yeast extracts whilst polyoxyethylenesorbitan monooleate, magnesium and manganese sulphates act as growth stimulants. Selectivity against streptococci and moulds is provided by ammonium citrate and sodium acetate. Used at low pH, ammonium citrate allows growth of lactobacilli whilst inhibiting a number of other organism groups. Occasionally, sterilisation of this medium at 121°C can cause the pH to fall outside of the specified pH limits 5.7 ±0.1. In these rare cases adjustment of the medium using acetic acid or sodium hydroxide is recommended.

• Analyte: lactobacillus spp.
• Platform: dehydrated culture media
• Formula: enzymatic digest of casein 10.0g/L, meat extract 10.0g/L, yeast extract 4.0g/L, triammonium citrate 2.0g/L, sodium acetate 5.0g/L, magnesium sulphate heptahydrate 0.2g/L, manganese sulphate tetrahydrate 0.05g/L, dipotassium hydrogen phosphate 2.0g/L, glucose 20.0g/L, polyoxyethylenesorbitan monooleate 1.08g/L, agar 15.5g/L
• Grams per litre: 70.00
• Litres per 500g: 7.00
• Plates per 500g: 390.00