Gram staining was invented by Danish physician Christain Gram in 1884 and is a widely used method of identification in bacteriology. The bacteria could be identified as gram-positive bacteria (G+) and Gram-negative bacteria (G-). The different color reaction of bacteria is due to the difference of cell wall permeability to ethanol and anti-decolorization ability, which is mainly determined by the thickness and structure of peptidoglycan layer.

This staining kit is modified from the original Gram staining method and is especially suitable for identifying bacterial infection in tissue sections. The bacteria are dyed dark purple or pink, and the background of the tissue is colored yellow by the redye solution, so that the bacteria present in the tissue can be clearly observed.