Phenolphthalein Phosphate Agar is recommended for identification of phosphatase positive Staphylococcus aureus. Such strains are coagulase-positive pathogenic strain, Phosphatase production is determined by the liberation of phenolphthalein, which is indicated by the change in colour of the medium, on alkali addition, the liberated phenolphthalein gives a bright pink-red colouration.