Correct Option: A

Gram +(ve) and Gram –(ve) bacteria are separated on the basis of their cell wall composition. Christian Gram, on the basis of staining behaviour of the cell wall with Gram’s stain, grouped bacteria into Gram +ve and Gram –ve type. The bacteria which retain blue or purple colour after staining are Gram +ve e.g. Bacillus subtilis and which loses blue colour is Gram –ve e.g. E. coli. In Gram –ve, stain is washed due to high lipid content in the cell having thick wall, Gram +ve has single layered cell wall rich in peptidoghycans which retain the colour.