Gram Staining Technique
Skill Lab
Gram Staining is the most important staining technique in microbiology (bacteriology),
developed by Danish physician Hans Christian Gram in 1884. It demonstrates the morphology
and distinguishes two bacterial categories:
Gram positive bacteria that stain dark purple
Gram negative bacteria stain light pink
Principle
Differences in Gram staining reaction between bacteria is thought to be due to differences
in the structure and permeability of the cell wall of Gram positive and Gram negative
organism. The Gram positive bacteria have a thick peptidoglycan layer and lower lipid
content than Gram-negative bacteria, which holds fast the basic dye crystal violet and resist
decolorization with acid alcohol. Following staining with basic dye and treatment with iodine,
the dye–iodine complex is not removed by decolorizer from the less permeable cell wall of
Gram positive bacteria, staining it blue/purple. Whereas in gram negative bacteria, the thin
peptidoglycan and more permeable cell wall of Gram negative bacteria allows easy removal
of Crystal violet stain by decolorizer and stained pink/red after counter staining with Safranin.
Skill Lab
Gram Staining is the most important staining technique in microbiology (bacteriology),
developed by Danish physician Hans Christian Gram in 1884. It demonstrates the morphology
and distinguishes two bacterial categories:
Gram positive bacteria that stain dark purple
Gram negative bacteria stain light pink
Principle
Differences in Gram staining reaction between bacteria is thought to be due to differences
in the structure and permeability of the cell wall of Gram positive and Gram negative
organism. The Gram positive bacteria have a thick peptidoglycan layer and lower lipid
content than Gram-negative bacteria, which holds fast the basic dye crystal violet and resist
decolorization with acid alcohol. Following staining with basic dye and treatment with iodine,
the dye–iodine complex is not removed by decolorizer from the less permeable cell wall of
Gram positive bacteria, staining it blue/purple. Whereas in gram negative bacteria, the thin
peptidoglycan and more permeable cell wall of Gram negative bacteria allows easy removal
of Crystal violet stain by decolorizer and stained pink/red after counter staining with Safranin.
