Microbiology Procedure

Index >> Staining Methods in Microbiology >> Stains For Fungi

Stains For Fungi

	Stains For Fungi The fungi constitute a group of microorganisms that is of great practical and scientific interest to microbiologists. Fungi are very diverse in their morphological manifestation. Generally speaking, fungi include the molds and the yeasts. Fungi are eukaryotic chemoorganotrophic microorganisms. They reproduce naturally by means of spores, with few exceptions.
Microscopic observation of spores and their arrangement is very important in the classification of fungi and in diagnosis of various infections of man, animals and plants. Fungi are also important in industrial fermentations. Readers may refer the books by Ainsworth and Sussman (15), Alexopoulos (16) and Stevens (17) for further details. Heat fixed, dry and Gram stained smears are satisfactory only for specimens containing yeasts, yeast like fungi and the larger yeast forms of dimorphic fungi. For the small yeast forms of Histoplasma capsulatum, alcohol fixed preparation are necessary to stain with Giemsa's stain which is described under the heading Romanowsky stains
Specimens that might contain either fungi or actinomycetes should be examined as wet mount preparation or agar block preparation as well as in smear preparation after staining with Gram stain or Ziehl-Neelsen acid-fast stain. Staining of fungal elements with lactophenol blue in wet mount preparation and in agar block preparation is the routine method available for microscopic examination. The modified periodic acid Scihiff stain is recommended for th direct observation of fungi in tissue sections. In this method, take the sections down to water. Wash in distilled water and immerse in periodic acid solution (S47) for 5 minutes. Wash the sections in tap water for 15-minutes and then rinse in distilled water. Immerse the sections in Schiffs reagent (S43) for 15 minutes.
Wash with two or three changes of freshly prepared sulphite wash solution (S50) for 5 minutes each. Wash in running water for 10 minutes, rinse in distilled water and blot. Counterstain with 0.002% malachite green or light green for 30-60 seconds. Rinse in water, dehydrate in absolute alcohol, clear in xylene and mount in Canada balsam. Fungi will appear red while nuclei and cytoplasm will appear green in colour.

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