Explain Differential Staining Technique?
It divides bacteria into separate groups based on staining properties, like Gram's stain, Acid-fast stain etc. Here 2 or more contrasting stains are used. It is also used to visualize cell structures, like flagella stain, capsule stain, spore stain, etc. In differential staining at least 3 chemical reagents are used. First stain is called the primary stain and it imparts colour to all the cells. Second reagent is called decolourizing agent which may or may not remove the colour of the primary stain from the entire cell or part of the cell, depending upon the chemical composition of the cell. Third reagent is called the counter stain which has a contrasting colour to primary stain and does impart colour to the those cells or their parts which are decolourized by decolourizing agent. Cells which retain the primary stain cannot absorb the counter stain. In this way, cell types or their structures can be distinguished from each other on the basis of the stain that is retained. In some cases, another chemical reagent called mordant is also used to increase cell's affinity for a stain.