Mannitol Salt Agar

Selectively and differentially isolate and identify staphylococci from clinical and non-clinical samples using Thermo Scientific™ Remel™ Mannitol Salt Agar. This phenol red mannitol agar contains 7.5% sodium chloride as a selective agent as reported by Koch in 1942¹. Most strains of coagulase-positive staphylococci grow on this agar, producing yellow zones because of mannitol fermentation whereas coagulase-negative staphylococci strains produce small colonies with no color change in the surrounding medium.

Staphylococci are widespread in nature, although they are mainly found on the skin, skin glands and mucous membranes of mammals and birds. The coagulase-positive species i.e., Staphylococcus aureus is well documented as a human opportunistic pathogen. The ability to clot plasma continues to be the most widely used and accepted criterion for the identification of pathogenic staphylococci associated with acute infections².

Mannitol Salt Agar is a selective and differential solid media for isolating staphylococci bacteria by using their capability to ferment mannitol by the production of coagulase enzyme.

• Easy to differentiate: Differentiates between coagulase-positive and coagulase-negative staphylococci.
• Selective: Sodium chloride in the concentration of 7.5% inhibits many bacteria other than staphylococci.

This medium contains peptones and beef extract, which supply nitrogen, vitamins, minerals, and amino acids essential for growth. The 7.5% concentration of sodium chloride results in the partial or complete inhibition of bacterial organisms other than staphylococci. Sodium chloride also supplies essential electrolytes for transport and osmotic balance. Mannitol is the fermentable carbohydrate, fermentation of which leads to acid production, detected by phenol red indicator, and aids in the differentiation of staphylococcal species. Coagulase positive staphylococci produce yellow colonies and a surrounding yellow medium while coagulase negative staphylococci produce red colonies and no color change of the phenol red indicator. Agar is the solidifying agent.

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