Microsporidia and Candida spores: their discrimination by Calcofluor, trichrome-blue and methylene-blue combination staining.

Abstract

Faeces of immunocompromised patients are often contaminated with the chitin-containing spores of microsporidia and Candida, which exclude the use of the chitin-specific fluorescent brightener Calcofluor white M2R for the identification of microsporidian spores. We developed a combination staining of Calcofluor white M2R with modified trichrome-blue staining and subsequent methylene-blue incubation which permits discrimination between these two types of spores. As a basis for diagnosis, a difference in the fluorescence pattern (365-440 nm) is combined with a difference in the light microscopic staining pattern. Under fluorescence conditions microsporidia spores have a spotted, brilliant white Calcofluor fluorescence and can easily be identified, while Candida spores show a reddish purple colour. Under the light microscope microsporidian spores show a light red colour with nonstained vacuole spots or strips in contrast to the yeast spores with their red-brown colour. This combination technique offers a highly specific means for the diagnosis of microsporidia spores in faeces.