Gram's stain

noun

ˈgramz- 

variants or Gram stain

ˈgram- 

1

: a method for the differential staining of bacteria by treatment with a watery solution of iodine and the iodide of potassium after staining with a triphenylmethane dye (such as crystal violet)

called also Gram's method

2

: the chemicals used in Gram's stain

Word History

Etymology

Hans C. J. Gram †1938 Danish physician

First Known Use

1903, in the meaning defined at sense 1

Medical Definition

Gram's stain

noun

variants or Gram stain

ˈgram- 

1

: a method for the differential staining of bacteria that involves fixing the bacterial cells to a slide and staining usually with the basic dye crystal violet, treating with an iodine solution to fix the dye, washing with acetone or alcohol to decolorize the dye, and counterstaining usually with a red safranine dye which shows up only if the crystal violet has been decolorized, that results in gram-positive bacteria retaining the purple dye and gram-negative organisms having it decolorized so that the red counterstain shows up, and that is believed to depend on differences in the structure and composition of the bacterial cell walls which facilitate or prevent the decolorization of the crystal violet dye by the alcohol or acetone

called also Gram's method

2

: the chemicals used in Gram's stain