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The decolorization step is critical and must be timed correctly; the crystal violet stain is removed from both gram-positive and negative cells if the decolorizing agent is left on too long (a matter of seconds). [19] After decolorization, the gram-positive cell remains purple and the gram-negative cell loses its purple color. [19]
Violet-stained gram-positive cocci and pink-stained gram-negative bacilli. In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
The gram-positive cocci are a large group of bacteria with similar morphology. All are spherical or nearly so, but they vary considerably in size. Members of some genera are identifiable by the way cells are attached to one another: in pockets, in chains, or grape-like clusters.
The negatively charged cell wall of many microorganisms attracts the positively charged chromophore which causes the specimen to absorb the stain giving it the color of the stain being used. Positive staining is more commonly used than negative staining in microbiology. The different types of positive staining are listed below. [1]
Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet during Gram staining, resulting in a purple color. Gram-negative bacteria have a thin peptidoglycan layer which does not retain the crystal violet, so when safranin is added during the process, they stain red.
One commonly recognizable use of differential staining is the Gram stain. Gram staining uses two dyes: Crystal violet and Fuchsin or Safranin (the counterstain) to differentiate between Gram-positive bacteria (large Peptidoglycan layer on outer surface of cell) and Gram-negative bacteria. Acid-fast stains are also differential stains.
The Gram-positive cell wall is characterized by the presence of a very thick peptidoglycan layer, which is responsible for the retention of the crystal violet dyes during the Gram staining procedure. It is found exclusively in organisms belonging to the Actinomycetota (or high %G+C Gram-positive organisms) and the Bacillota (or low %G+C Gram ...
The outer red layer in this diagram is the capsule, which is distinct from the cell envelope. This bacterium is gram-positive, as its cell envelope comprises a single cell membrane (orange) and a thick peptidoglycan-containing cell wall (purple). The bacterial capsule is a large structure common to many bacteria. [1]