Fundamentals of Microbiology

Background

Bacteria can be differentiated based on Gram staining technique which will aid in identification of bacteria. Of all the staining techniques, Gram staining is the most important tool in identification of bacteria.

This technique was developed by Danish bacteriologist, Christian Gram in 1884. This technique separates bacteria into two groups: those that are gram-positive and those that are gram-negative. The procedure is based on the ability of microorganisms to retain the purple colour of crystal violet during decolourization with alcohol. Gram- negative bacteria are decolourized by alcohol losing the purple colour of crystal violet. Gram-positive bacteria are not decolourized and remain purple. After decolorization, safranin, a red counter-stain is used to impart a pink colour to the decolourized gram-negative bacteria.