The Gram’s staining (Differential staining) method is responsible for classifying the bacteria into two broad groups i.e., Gram Positive bacteria and Gram Negative bacteria according to the stains they take up during the staining procedure.
The bacteria which take up the crystal violet stain and are stained violet-blue in colour are called as Gram-positive bacteria. The cell walls of gram positive bacteria are thick and are mainly composed of proteins and mucopeptides.
During Gram’s staining, the crystal violet is the primary stain. After the application of a mordant i.e., Gram’s Iodine, a cell is more strongly stained. When treated with alcohol, it causes dehydration and closure of the cell-wall pores, thereby the Crystal-violet iodine complex (CVI) formed remains inside and here the cell remains violet in colour and does not take up the counter stain.
Some examples of Gram Positive bacteria are: Bacillus subtilis, Saccharomyces cerevisiae, Staphylococcus aureus, Clostridium tetani, Corynebacterium diphtheriae
