Gram Staining reaction

Gram staining is the most useful staining procedure used in bacterial identification schemes. It separates almost all medically important bacteria into two general types: gram-positive bacteria, which stain a deep purple color, and gram-negative bacteria, which stain a pink to red color.

This difference in reaction to the Gram stain arises because of differences in the cell wall of gram-positive and gram-negative cells.

Preparation of Gram stain Reagents

Preparation of Gram stain Reagents

Reagents are primary stain (crystal violet), mordant (iodine), decolorizer (ethanol or acid-alcohol), and counterstain (safranin or dilute carbol-fuchsin).

Gram Staining: Principle, Procedure, Results

Gram Staining: Principle, Procedure, Results

Gram-positive bacteria retain the crystal violet-iodine complex and stain purple, whereas gram-negative bacteria stain pink.

Gram-Positive vs. Gram-Negative Bacteria

Gram-Positive vs. Gram-Negative Bacteria

Gram positive bacteria appear purple and gram-negative bacteria appear pink when stained by Gram-staining methods.

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Importance of Gram Stain in Anaerobic Bacteriology

Positive gram stain with negative culture report gives information regarding the adequacy of sample collection, transport, and also of culture methods used.

Variations in Gram Staining Results

Variations in Gram Staining Results