Spore stain

 

Some Gram-positive bacteria produce endospores which are highly resistant to heating and a variety of chemicals. These spores are found in the genera Bacillus and Clostridium. The spores are difficult to stain using normal techniques, but it is possible to drive the stain into them using heat. Once the stain has been taken up by the spores, it is extremely difficult to decolourise them, although the vegetative portion of the cell can be decolourised easily. Several versions of the spore stain are used.