The staining of oocysts of cryptosporidium with the fluorescent brighteners uvitex 2B and calcofluor white

Abstract

Background: There have been only 2 reports that Cryptosporidium oocysts fluoresce with the fluorescent brightener (FB) Uvitex 2B (U2B), and none with the more commonly used FB calcofluor white (CFW). Methods: Smears of formalin-fixed feces containing Cryptosporidium oocysts were examined with U2B and 3 CFW products under a variety of conditions of concentrations, pH, staining times, and temperatures. Results: Under the conditions that a wide range of fungal and parasite structures, including spores of the microsporidia, fluoresce well with CFW and U2B (ie, 0.05% to 0.1% solutions at neutral or at alkaline pH at room temperature), oocysts were not found to fluoresce. However, staining with alkaline solutions for 2 minutes at 60°C to 65°C produced oocyst fluorescence ranging from bright to minimal, even within the same smear. Conclusions: Any of the FB reagents tested could be used as a simple and rapid stain procedure for Cryptosporidium oocysts in fecal smears.