Phosphatase activity of staphylococci is constitutive in some species and repressed by phosphates in others.
The phosphatase activities of colonies of staphylococcal strains belonging to the 10 species most frequently isolated from specimens of human origin were evaluated on media with undetermined inorganic phosphate contents and on media supplemented with known amounts of phosphates. All strains of all species tested were phosphatase positive on plates that were not supplemented with inorganic phosphates when the pH of the medium was high. In media supplemented with 0.3% phosphates at low and high pH, all strains of Staphylococcus aureus, almost all strains of S. epidermidis and S. xylosus, and none of the other species tested were phosphatase positive. Thirty S. simulans strains were grown in broths at pH 7 with and without phosphates, and the phosphatase activities of the cells were assayed at pH 5.5 and 8 in the absence of phosphates. At pH 8, all strains gave a strong positive reaction when grown in the absence of phosphates and a negative reaction when grown in the presence of these salts at 0.3%. It was concluded that all the species of staphylococci tested possess phosphatase activity and that the staphylococcal phosphatases are constitutive in some species and repressed in others.