Question

When a cell containing an endospore (such as Bacillus subtilis) is stained with the Gram's method, the cell is stained but the endospore is clear. How can you account for these results?

Answer 1

Endospores Staining

Endospores are substances that are formed inside of specific bacterial cells which boost their survival rate in times of harsh conditions.

Gram staining alone is not sufficient to observe the endospores, which seems apparently clear when Gram-stained cells are observed.

Endospore staining employs two stains to identify endospores from other cell components.

•The Schaeffer-Fulton method employs heat to promote the primary stain (malachite green) into the endospore. Rinsing with water will well wash away the colour from the cell, as the endospore still appears to be green stained. Counterstaining pink with safranin will show the shape and location of endospores, if they are a part of the cell. The green endospores will be seen inside the pink vegetative cells or it will appear distinct from the pink cells in total. If no endospores are seen, only the pink vegetative cells will be observable.

The attached image shows a stained preparation of Bacillus subtilis revealing the endospores as green and its vegetative cells in pink coloration.

Endospore-staining procedures are essential for observing Bacillus and Clostridium, two genera of endospore-forming bacteria, production of bioterrorism agent from B. anthracis (which causes anthrax.