Gram Staining Quiz

Gram Staining Procedure and Differences Between Gram Positive and Gram Negative Bacteria

• The Gram staining method was developed by Danish Physician Christian Gram in 1884
• It is a differential staining procedure that classifies bacteria into two classes - Gram positive and Gram negative
• Gram positive bacteria retain crystal violet and appear dark violet, while Gram negative bacteria lose the crystal violet and appear red when counterstained by safranin
• Gram positive cell walls contain teichoic acid, teichuronic acid, and polysaccharide molecules
• Gram negative cell walls contain lipoprotein, outer membrane, and lipopolysaccharide
• Gram positive cell walls are thick layered (0.015 μm-0.02μm) and rigid due to the presence of peptidoglycans
• Gram negative cell walls are thin layered (0.0075μm–0.012μm) and elastic due to the presence of a lipoprotein-polysaccharide mixture
• The chemical composition of Gram positive bacteria is 80% peptidoglycans, 20% polysaccharide, and the presence of teichoic acid, while Gram negative bacteria contain 3 to 12% peptidoglycans and rest is polysaccharides and lipoproteins, with teichoic acid absent
• Gram negative bacteria have an outer membrane and periplasmic space, which are absent in Gram positive bacteria
• The differences between Gram positive and Gram negative bacteria are summarized in Table 1.6
• The Gram staining procedure involves specific steps, as illustrated in Figure 1.10
• This staining method is crucial for differentiating between the two types of bacteria based on their cell wall characteristics