These differences in the cell walls of Gram-positive and Gram-negative bacteria are classified according to their composition, cell structure as well as the activity of the Gram-staining method.
The cell wall is the outermost and inorganic part of the cell. It is found in plant cells, fungi, bacteria and algae. Cell walls are thicker, harder and more elongated which helps them increase in thickness over time. The cell wall is metabolically inactive because it lacks receptors and is mostly tangled.
- Providing a fixed shape to the cell.
- Protecting the cell from the external environment.
- Acting as a barrier between the external and internal environment.
Depending on the thickness of the cell wall, bacteria are classified as Gram-positive and Gram-negative bacteria. They can be distinguished by gram staining.
Gram-positive bacteria are a distinct group of bacteria that appear purple when stained with Gram stain and examined under the microscope Clostridium, Actinomyces, Mycobacterium, Nocardia, Streptococci, and Staphylococci are some examples of Gram-positive bacteria.
Gram-negative bacteria are a distinctive group of bacteria that appear pink when Gram-stained and examined under the microscope Vibrio, Campylobacter, and Pseudomonas are some examples of Gram-negative bacteria.
| Gram-Positive Cell Wall | Gram-Negative Cell Wall |
| Layers | |
| Single layered | Double layered |
| Composition | |
| Consisting of several layers of peptidoglycan | Consisting of a single layer of peptidoglycan |
| Thickness | |
| 15 to 80 nanometers | 10 nanometers |
| Periplasmic space | |
| Small | Large |
| Outer membrane | |
| Absent | Present |
| Teichoic Acid | |
| Present | Absent |
| Porins | |
| Absent | Present |
| Lipid Content | |
| Very low (2 – 5 per cent) | High (15-20 per cent) |
| Lipopolysaccharides | |
| Absent | Present |
| Gram staining Procedure | |
| Retains the crystal violet dye and appears purple in colour | It does not retain the crystal violet dye and appears pink in colour |
