Peptidoglycan Layer: Gram-positive bacteria have a very thick, multi-layered peptidoglycan layer (20–80 nm), which retains the purple crystal violet stain. Gram-negative bacteria have a much thinner peptidoglycan layer (2–3 nm).

• Outer Membrane: Gram-negative bacteria possess a unique outer lipid membrane containing lipopolysaccharides (LPS) that is absent in Gram-positive bacteria.

• Chemical Components: Gram-positive cell walls typically contain teichoic acids, which are absent in Gram-negative bacteria.

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