Question

Bacterial cells can be stained with

• A. Methylene blue
• B. Safranin
  
• C. Crystal violet and iodine
• D. All of the above

Answer 1

Answer: (D)

All of the above

Methylene blue or Loefflers is used as a stain for determining bacterial morphology. It is a cationic dye that binds to negatively charged molecules inside the cell and gives blue colouration.

Crystal violet and iodine are popular dyes for staining (violet) Gram-positive bacteria as they have a thick peptidoglycan cell wall.

On the other hand, Gram-negative bacteria are counter stained by using safranin (pink).

Thus, the correct answer is option D.