Use MRS (ISO) Agar for enumeration and isolation of mesophilic lactic acid bacteria from food samples. MRS (ISO) Agar encourages the growth of the lactic acid bacteria, which includes species of the following genera: Lactobacillus, Streptococcus, Pediococcus, and Leuconostoc.

• Adheres to ISO 15214: 1998 standards.
• Superior performance over tomato juice medium of Briggs¹ and the meat extract tomato juice medium of de Man.

The MRS formulation was developed by de Man, Rogosa, and Sharpe² in 1960 to replace a variable component (tomato juice) and, at the same time, provide a medium which would support good growth of lactobacilli in dairy products, even those strains which showed poor growth in existing media.
MRS (ISO) Agar was designed to conform to the formulation specified in ISO 15214: 1998 Horizontal method for the enumeration of Mesophilic lactic acid bacteria―colony count technique at 30°C.
The medium shows some degree of selectivity, however, if yeasts and mold contamination in the food samples is of concern, these microorganisms can be inhibited by the addition of selective agents like sorbic acid, ciprofloxacin, or clindamycin.
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