Flow cytometric application of the Sabin and Feldman dye test in the diagnosis of toxoplasmosis

Although time-consuming and requiring live parasites, the Sabin and Feldman dye test (DT) is still considered the 'gold standard' among the serologica l tests for toxoplasmosis diagnosis. The present study was initiated to com pare detection of dead parasites using optical microscopy with flow cytomet ry and a fluorescent nonvital dye, propidium iodide. After incubation with sera (N = 150) and a complement source, tachyzoites were washed, then stain ed using a fluorescein-conjugated Toxoplasma-specific antiserum. Dead tachy zoites were detected by flow cytometry after addition of propidium iodide. Intra- and inter-assay reproducibilities of percentages of dead parasites v aried between 7 and 14%, and 8 and 21%, respectively. When comparing flow c ytometry with the classical DT, no discrepancy was noted for positive (N = 118) and negative sera (N = 32), Correlation was good (r = 0.85) for positi ve sera. in conclusion, when easily available, flow cytometry is a very sen sitive, specific and time-sparing method to detect specific antibodies to T oxoplasma gondii. (C) 1999 Elsevier Science B.V. All rights reserved.