Final answer:
Safranin is used as a counterstain in the Gram staining method to distinguish Gram-negative cells, which it stains pink, after decolorization. It is also used in endospore staining to counterstain vegetative cells.
Step-by-step explanation:
Safranin is used in the Gram staining method as a counterstain. During the Gram staining process, after the cells are stained with crystal violet and then decolorized, Gram-negative cells are left colorless. The addition of safranin stains these decolorized cells pink, allowing for the differentiation between Gram-positive and Gram-negative cells. The primary stain for Gram-positive cells is crystal violet, which is trapped in the cells by the mordant, iodine. Meanwhile, in endospore staining methods, such as the Schaeffer-Fulton method, safranin serves a different purpose: it is used as a counterstain to stain vegetative cells pink after the endospores have been stained green with malachite green. This differential staining technique allows for the visualization of endospores within the bacterial cells or as separate entities.