The nutrient medium has a high concentration of sodium chloride of which amount has an inhibitory effect on most bacteria, but no effect on the growth of staphylococci. Because of this, the medium  is convenient to use for separation of staphylococci. In addition, the nutritional quality of the medium differentiates produce lecithinase staphylococci.

Colonies which produce lecithinase form a "rainbow" area, which is visible when the light is incident at an angle.