Question

Select the correct option:

Which of the given statements are correct?
(i) Bacillus subtilis is a Gram $(+)$ bacteria.
(ii) Escherichia coli is a Gram $(-)$ bacteria.
(iii) Washing of the Gram's stain in Gram $(-)$ bacteria is due to high lipid content of the cell wall, which gets dissolved in organic solvent like acetone.

• A. (i) and (ii)
• B. (ii) and (iii)
• C. (i) and (iii)
• D. (i), (ii) and (iii)

Answer 1

Answer: (D)

(i), (ii) and (iii)

Bacteria can be classified into two groups based upon reaction of bacteria to Gram's stain (Christian Gram, $1884$). Bacteria are first stained with weakly alkaline solution of crystal violet and then treated with $0.5$% iodine solution. This is followed by washing with water and then with alcohol or acetone.

Bacteria which retain blue or purple colour are known as Gram $(+)$ bacteria (e.g., Bacillus subtilis).

Bacteria which do not retain stain and become colourless are called Gram $(-)$ bacteria (e.g., Escherichia coli). Washing of the stain in Gram $(-ve)$ bacteria is due to high lipid content of their cell wall which gets dissolved in organic solvents like acetone.

So, the correct answer is '(i), (ii) and (iii)'.