Question

Gram-positive bacteria stain purple because

• A. The cell wall of Gram-positive bacteria is high in lipopolysaccharide
• B. The cell wall of Gram-positive bacteria is high in peptidoglycan
• C. There are 2 rings in the flagellar structure of the Gram-positive bacteria
• D. All of the above

Answer 1

The correct option is B

The cell wall of Gram-positive bacteria is high in peptidoglycan

Gram-positive bacteria retain crystal violet dye and stain dark violet or purple, that is, they remain coloured blue or purple with Gram stain when washed with absolute alcohol and water. In a Gram stain test, bacteria are washed with a decolourising solution after being dyed with crystal violet. On adding a counterstain such as safranin or fuchsin after washing, Gram-negative bacteria are stained red or pink while Gram-positive bacteria retain their crystal violet dye. This is chiefly due to the difference in the structure of their bacterial cell wall. The peptidoglycan cell wall is thicker in Gram-positive bacteria, which retains the colour of crystal violet, while the peptidoglycan layer is thinner in Gram-negative bacteria. The cell wall of Gram-positive bacteria is high in peptidoglycan which is responsible for retaining the crystal violet dye.