Note on the Use of Evans Blue as a Background Stain in the F.T.A. Test
Catherine L. Fry, Alan E. Wilkinson · Sexually Transmitted Infections · 1963
Treponeme suspensions for use in the Fluorescent Treponemal Antibody (FTA) test are usually pre- pared in the protein-containing basal medium used in the Treponemal Immobilization (TPI) test.Such suspensions sometimes show fluorescent staining of debris in the background which may make it difficult to assess the intensity of fluorescence shown by the treponemes, especially with tests on sera showing borderline reactivity.It was thought that, if the background could be stained a constrasting colour to the apple-green fluorescence of the treponemes, the reading of results might be made easier.The use of Evans blue as described by Nichols and McComb (1962) with trachoma and related antigens was investigated.This dye fluoresces red under ultra- violet light and thus affords a good contrast to the specific green fluorescence.