In the previous post we discussed the unique properties of endospores. These unique properties mean that they are not easily penetrated by stains. If endospore containing cells are stained by crystal violet, the spores appear as unstained areas in the vegetative cell. If heat is applied while staining with malachite green, the stain penetrates the endospore and green is not removed by subsequent washing with decolorizing agents or water. In this situation heat is acting as a mordant much like iodine in a gram stain procedure. There are two methods for spore staining. The Schaeffer-Fulton method uses malachite green to stain the endospore and safranin to stain the vegetative portion of the cell. A properly stained spore forming cell will have a green endospore contained in a pink sporangium. The Dorner method produces a red spore with a colorless sporangium. Nigrosin is used to provide a dark background. Both the sporangium and endospore are stained however the safranin diffuses out of the sporangium and into the nigrosin leaving a colorless sporangium.
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