Mannitol salt agar is a selective, differential growth medium used for the culture of staphylococcus bacteria capable of fermenting mannitol which is the principal sugar source. The medium contains mannitol as the sugar source and (7.5 - 10%) sodium chloride which inhibits the growth of most other bacteria, phenol red; an indicator for detecting pH change produced due to mannitol fermentation. The fermentation of mannitol by the bacteria causes the production of an acidic byproduct changing the colour of the medium to change from pink/red to yellow.
