They are stained purple with this staining technique. They form a CV- 1 complex (Crystal violet complex 1) and retain the primary dye color. Gram-positive bacteria have a simple cell wall. IT has a large amount of fo peptidoglycan. It has a lesser amount of lipopolysaccharide.
Examples: Staphylococcus, Bacillus, Corynebacterium
There are following characteristics are generally present in a Gram-positive bacteria:
- They have cytoplasmic lipid membranes.
- Gram-positive bacteria have only one membrane layer.
- They have a thick peptidoglycan layer. Teichoic acid and lipids are present. They form lipoteichoic acid. It acts as chelating agents. It also used for certain types of adherence.
- Capsule polysaccharides (only in some species).
- Flagellum (only in some species) it present, it contains two rings for support.
They are stained pink with this staining technique. They retain secondary dye color. Gram-negative have a lesser amount of peptidoglycan. It has a more complex structure. An outer membrane of lipopolysaccharides is present outside the layer of peptidoglycan. Gram-negative species are more dangerous than gram-positive bacteria. The lipopolysaccharide layer is often toxic. This layer protects the bacteria from the immune system of the host. Gram-negative bacteria are more resistant to antibiotics. Its examples are pseudomonas. There are the following characteristics of Gram-negative bacteria:
- They also have a cytoplasmic membrane
- They have thin peptidoglycan layer(much thinner than in Gram-positive bacteria)
- The outer membrane containing lipopolysaccharide outside the peptidoglycan layer
- Porins exist in the Outer Membrane. It acts like pores for particular molecules.
- There is a space gap b/w secondary cell membrane and layers of peptidoglycan. It is called the periplasmic space.
- The S-layer is directly attached to the outer membrane, rather thane the peptidoglycan.
- If present, flagella may have 4 supporting rings instead of 2.
- No teichoic acids are lipoteichoic acids are present
- Lipoproteins are attached to the polysaccharide backbone
Cell Wall Difference in Table
|Component||Gram-Positive Bacteria||Gram-Negative Bacteria|
Inner Rigid wall layer
|Outer layer wall|