Mannitol salt broth is used for the selective isolation of pathogenic staphylococci. This medium is recommended for the detection and enumeration of coagulase-positive Staphylococci in milk, food and other specimens. Mannitol salt broth is used for the isolation of suspected pathogenic Staphylococci. Pathogenic staphylococci ferment mannitol and produce a yellow-coloured medium. The medium contains HM B peptone and protein peptone, making it highly nutritious as they provide essential growth factors and trace elements. Many other bacteria, with the exception of staphylococci, are inhibited by 7.5% sodium chloride. Mannitol is the source of fermentable carbohydrates. The differential action of the medium is attributed to D-Mannitol. Staphylococcus aureus ferments mannitol to produce a yellow-coloured medium. Most species of coagulase-negative Staphylococcus and Micrococci do not ferment mannitol and therefore the medium remains red in color. The color of the medium is due to the reactivity of phenol red at the pH of the medium; phenol red is red at pH 8.4 and yellow at 6.8. Suspected Staphylococcus with a yellow colored medium should be further tested for coagulase production.