Mannitol Salt Broth

Because of the amount of peptones and beef extract, Mannitol Salt is a nutrient rich medium. Most bacteria (other than straphylococci) are inhibited by the high concentration of sodium chloride. Organisms capable of fermenting mannitol, e.g. Staphylococcus aureus, cause a pH change in the media. With phenol red as the pH indicator the colonies appear with a yellow coloration.