Question

Bacteria which retain purple colour after staining with gram stain is
A. Gram +ve
B. Gram –ve
C. Trichous
D. Spirillum

Answer 1

Hint:Gram staining is a method of separating bacterial species into two large groups (gram-positive and gram-negative). It is the first step in the identification of bacteria.

Complete answer:
There are many steps in the gram staining process:
Bacteria stained with crystal violet.
Bacteria will be stained purple.
Bacteria which are stained purple in the presence of gram iodine solution.
Stain will be fixed due to formation of a complex of crystal violet and iodine.
After this, Alcohol or acetone is added as a decolourizer.
Bacterial cells will be decolourized while some cells will retain the stain.
After this, these bacterial cells stained with the safranin (counter stain).
Cells that retain the colour of primary stain are called Gram positive.
Cells that do not retain the colour of primary stain and take up the colour of counter stain are called Gram negative.
Gram positive bacteria are the bacteria that give positive results in the gram stain test. Gram positive bacteria have a thick peptidoglycan layer and cytoplasmic lipid membrane.
Gram negative bacteria are the bacteria that give negative results in the gram stain test. Gram negative bacteria have a thin peptidoglycan layer.

So the correct answer is option A.

Note: Gram staining method is named after Hans Christian gram who developed this technique. It is a valuable diagnostic tool in clinical and research techniques but not all bacteria can be classified by this technique.