The bacillus Subtilis gram stain is a way to test if a patient is infected by the bacteria. Bacillus Subtilis is an endospore.
According to Textbook of Bacteriology, the bacillus Subtilis resists destaining and staining, meaning that it holds the dye placed into a patient's body and remains visible to tests once stained but is difficult to stain to begin with. Because of the ability to differentiate between diseases and infections through the dyes, several dying procedures, like the Schaeffer-Fulton staining method, can differentiate between the endospore and things like sporangia or vegetative cells. Endospores have a high resistance to chemicals and heat.