GRAM STAIN- part 2
Written on: Tuesday, July 28, 2009
Time: 8:21 AM
Time: 8:21 AM
Why do they stain differently? :
· Difference in chemical and physical structures of their cell walls.
· Gram-positive bacteria have a thick cell-wall. It consists of several interconnecting layers of peptidoglycan as well as some teichoic acids. Basically, 60% -90% of the gram-positive cell wall is peptidoglycan.
· A Gram-negative bacteria has a thin cell wall which 10%-20% consist of peptidoglycan but is surrounded by an outer membrane made up of phospholipids, lipopolysaccharide and lipoprotein.
· Addition of the decolourizer causes dehydration and shrinkage of the gram-positive cell wall, thus it can better retain the crystal violet-iodine complex.
· In gram-negative bacteria, adding the decolourizer ruptures the outer membrane and the stain gets washed out.
· Safranin added would only cause the gram-negative bacteria to be stained pink while gram-positive bacteria remains purple.
· Difference in chemical and physical structures of their cell walls.
· Gram-positive bacteria have a thick cell-wall. It consists of several interconnecting layers of peptidoglycan as well as some teichoic acids. Basically, 60% -90% of the gram-positive cell wall is peptidoglycan.
· A Gram-negative bacteria has a thin cell wall which 10%-20% consist of peptidoglycan but is surrounded by an outer membrane made up of phospholipids, lipopolysaccharide and lipoprotein.
· Addition of the decolourizer causes dehydration and shrinkage of the gram-positive cell wall, thus it can better retain the crystal violet-iodine complex.
· In gram-negative bacteria, adding the decolourizer ruptures the outer membrane and the stain gets washed out.
· Safranin added would only cause the gram-negative bacteria to be stained pink while gram-positive bacteria remains purple.
gram positive
gram negative