What is the secondary dye used in the endospore stain?

The secondary dye used in the endospore stain is safranin. In the endospore staining procedure, the primary dye, which is malachite green, is used to stain the endospores. After this, safranin is applied as a counterstain to stain the vegetative cells and the background. This technique allows for effective differentiation between endospores, which retain the green color, and the vegetative cells, which take up the red color of safranin.

The use of safranin as the secondary dye is critical because it enhances visual contrast in microscopy, allowing for easier identification of both endospores and the surrounding non-spore cells. Other compounds such as methylene blue, carbol fuchsin, and crystal violet serve different purposes in other staining procedures and are not utilized in this specific context of endospore staining. Therefore, safranin is the correct choice as it serves its specific role in the staining protocol effectively.