Malachite green spore stain uses heat to drive the primary stain into endospores. After decolorization with water, the counterstain safranin colors vegetative bacterial cells red. The endospores appear:

• A Red, since they retain the counterstain after decolorization
• B Colorless/unstained, as neither stain penetrates the spore coat
• C Blue-black, due to the dipicolinic acid–calcium complex within the spore
• D Green, as malachite green is retained within the endospore's resistant coat and is not decolorized by water washing ✓

Explanation

In the Schaeffer-Fulton spore stain, malachite green is driven into the spore by steam heating, where it binds tightly to spore components. Water (the decolorizer) readily removes malachite green from vegetative cell cytoplasm but cannot decolorize the spore because the dense cortex and spore coats resist re-extraction. Vegetative cells are then counterstained pink/red with safranin. Endospores therefore appear green against a red background of vegetative cells.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.