A test for bacterial alkaline phosphatase: use in rapid identification of Serratia organisms.

This investigation concerns identification of alkaline phosphatase production by bacterial organisms, as detected by a blue color resulting from conversion of indolyl phosphate to indigo. Coagulase-positive Staphylococcus produced alkaline phosphatase; coagulase-negative Staphylococcus did not. Serratia did not produce alkaline phosphatase; those Enterobacteriaceae we tested did. Thus, this test rapidly differentiates these organisms, diminishing the time for identification of Serratia in the clinical laboratory by 48 h. Identification of Serratia should not be ignored, because it is a life-threatening complication for certain hospitalized patients.