The selective staining mechanism of phosphatase producing colonies in the diphosphatephenolphthalein-methyl green method for the detection of bacterial phosphatase activity.

The aim of this study was to explain, in a novel method for the testing of bacterial phosphatase activity (MGP), the mechanism by which, in the presence of a phosphatase substrate and a stain, the phosphatase positive colonies become intensely pigmented while the others remain unstained (Satta et al., 1979). The experiments here described indicate that the products of the phosphatase reaction form, with the stains, high pigmented insoluble complexes that precipitate at the site where the reaction has occurred. Since, in most bacteria, phosphatase are membrane bound, in the presence of phosphatase substrates and stains, intensely stained precipitates are formed on his bacterial component. Such precipitates make the cells become stained and cause the intense pigmentation of the phosphatase positive colonies.