Gram staining = a method of staining the cell walls of bacteria to aid their identification.
Prior to gram staining, all bacteria are colourless. Then...
Gram-positive bacteria = purple.
Gram-negative bacteria = purple.
- The cell wall of bacteria is a 3D network of peptidoglycan. The cross-linking of these molecules provides strength and gives bacteria their unique shape.
- The cell wall also protects agains swelling/bursting or lysis caused by the osmotic uptake of water.
- Gram-positive bacteria have the basic cell wall structure. HOWEVER, gram-negative bacteria have an additional outer layer of lipopolysaccharide.
How does gram staining work?
1. Crystal violet, a basic dye, is added to the bacteria. This binds to the peptidoglycan layer, so all bacteria stain…