Fundamentals of Microbiology

2.3.2.3 Gram Staining

The simple staining procedure makes to visualize bacteria clearly, but it does not distinguish between organisms of similar morphology. In 1884, a Danish Physician named, Christian Gram discovered a new technique to differentiate the bacteria of similar morphology. He used two dyes in sequence, each of a different colour. The organisms that retain the colour of the first dye are called Gram positive and those that cannot retain the first dye when washed with a decolourizing solution, but then take on the colour of the second dye are called Gram negative.