Gram Stain Results

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.

Gram Negative Cocci Gram Negative Rods Gram Positive Cocci Gram Positive Rods

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