Purpose: To differentiate between Gram-positive
and Gram-negative organisms, while simultaneously learning about the cellular
morphology and arrangement.
Principle: Gram-positive cells
have a thick peptidoglycan cell wall that is able to retain the crystal
violet-iodine complex that occurs during staining, while Gram-negative
cells have only a thin layer of peptidoglycan. Thus Gram-positive
cells do not decolorize with ethanol, and Gram-negative cells do decolorize.
This allows the Gram-negative cells to accept the counter stain safranin.
Gram-positive cells will appear blue to purple, while Gram-negative cells
will appear pink to red.
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