A common medium used for the isolation of pathogenic staphylococci is the Mannitol Salts Agar. The high salt concentration of this medium inhibits the growth of most other organisms. Pathogenic staphylococci not only grow on the medium, but they also produce acid from it. This acid production turns the pH indicator from red to yellow. Non-pathogenic staphylococci can grow on the medium but produce no acid from it.
