Mannitol Salt Agar

Mannitol Salt Agar is a modified version of the selective agar proposed by Chapman (1945) for the isolation and presumptive identification of Staphylococcus aureus. The medium supports the growth of Staphylococcus aureus, whereas its high salt content (7.5%) inhibits the growth of many other microorganisms. In contrast to most other Staphylococci, coagulase-positive S. aureus can build acids from mannitol. Therefore, they build up yellow colonies with yellow zones. Beef extract, a pancreatic digest of casein, and animal tissue in the media provide carbon, nitrogen compounds, long-chain amino acids, vitamins, trace nutrients and other essential growth factors. Phenol red indicator aids in the detection of acid produced by fermentation of mannitol.

The Mannitol Salt Agar media is recommended for the isolation and presumptive identification of Staphylococcus aureus in non-sterile pharmaceuticals and foods. However, the coagulase test will need to confirm the findings.