The major difference between the cell walls of gram-positive and gram-negative bacteria lies in their structure and composition, specifically in the layers of peptidoglycan and the presence of additional membranes.
In gram-positive bacteria, the cell wall is primarily composed of a thick layer of peptidoglycan, which provides structural support and rigidity. This layer can be up to 90% of the cell wall’s composition and is responsible for retaining the crystal violet stain used in the Gram staining procedure, giving these bacteria their characteristic purple color.
On the other hand, gram-negative bacteria have a much thinner peptidoglycan layer, which typically constitutes only about 10% of their cell wall. Instead, they are surrounded by an outer membrane that contains lipopolysaccharides (LPS). The presence of this outer membrane is a key defining feature of gram-negative bacteria and plays a significant role in their increased resistance to certain antibiotics and the immune response.
To summarize, the main differences are:
- Thickness of Peptidoglycan: Gram-positive bacteria have a thicker peptidoglycan layer compared to gram-negative bacteria.
- Outer Membrane: Gram-negative bacteria have an additional outer membrane that gram-positive bacteria lack.