Gram staining
Japanese: グラム染色
A staining method that classifies bacteria into two groups based on cell wall structure. Gram-positive bacteria retain crystal violet dye, while Gram-negative do not. Devised by Hans Gram in 1884.
Gram staining is a fundamental method for dividing bacteria into two groups. Devised in 1884 by Danish bacteriologist Hans Gram, it involves staining with a purple dye called crystal violet, then decolorizing with alcohol. If purple remains, the bacterium is Gram-positive; if decolorized, Gram-negative.
This difference stems from cell wall structure. Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative have a thin layer plus an outer membrane. Lactic acid bacteria and natto bacteria are positive; acetic acid bacteria and E. coli are negative.
A technique from over 140 years ago still serves as the first step in microbiology. Its simplicity and utility transcend time.