Methods to maximise the staining of fungal propagules with fluorescent dyes

The spores and conidia of most fungi have very thick and resistant cell walls that severely impede the staining with fluorescent dyes to allow epifluorescence microscopy to be employed for their direct detection and quantification in natural habitats. In this study, oxidation by sodium hypochlorite and microwave irradiation (MWI) were used to enhance the staining of Aspergillus fumigatus and Penicillium brevicompactum conidia with six fluorescent dyes. Sodium hypochlorite resulted in high percentages of stained conidia (up to 98.8% with 4' 6-diamidino-2-phenylindole [DAPI]), but had to be removed prior to staining with consequent heavy conidia losses. By contrast, MWI gave very high percentages, while its enhancement of fluorescence intensity facilitated observation by epifluorescence microscopy. (C) 2004 Elsevier B.V. All fights reserved.