Used as a selective and differential medium primarily for the isolation and identification of Staphylococcus species, especially Staphylococcus aureus, from clinical and non-clinical samples. The high salt concentration inhibits the growth of most Gram-positive and Gram-negative bacteria except staphylococci and some enterococci. Mannitol fermentation by certain staphylococci, such as S. aureus, produces acid, which lowers the pH and causes a color change in the phenol red indicator, helping differentiate fermenters from non-fermenters. Commonly used in clinical labs to screen for pathogenic staphylococci in wound, food, and environmental samples.