B'coz gm positive bacteria get stained with the colour of safranine...
Gram-positive cells are purple and the Gram-negative cells are red.
The major difference between gram positive and the gram negative bacteria is the structure of their cell wall. The gram positive bacteria have two layers a plasma membrane and outer to it a peptidoglycan layer. But the gram negative bacteria have another layer other than the cell wall. While the gram negative bacteria has three layers. It has a plasma membrane that is called as the inner membrane, then a peptidoglycan layer and finally an outer membrane of phospholipids and lipopolysaccharides. There is space between the inner membrane and the peptidoglycan layer called as the periplasmic space. Peptidoclycan layer in the gram positive bacteria are much more thicker than that of the gram negative bacteria. The molecule teichoic acid is present in gram positive bacteria and the porin proteins are characteristically present in the gram negative bacteria. Gram positive bacteria usually produce exotoxins and the gram negative bacteria usually produces endotoxins. Gram positive bacteria gives Violet colour to the gram staining and the gram negative bacteria gives pink colour to the gram staining. In gram staining the bacteria is fixed on slides and then they are treated with Crystal Violet. After that they are treated with iodine and then they are decolourised. If the bacteria is gram negative then it shows Violet colour and if it is gram negative then it shows pink colour. Initially both strains show Violet colour after Crystal Violet treatment but on the treatment with iodine and decolourisation the gram negative bacteria loose colour and become pink. This is because in the gram positive bacteria the Violet crystals bind firmly to the peptidoglycan layer and the colour is not removed in later stages. In gram positive bacteria the colour does not penetrate much because of outer membrane and is lost much during decolourisation.
Gram-positive does not refer to a positive charge, but to the purple color of the stain. Gram-negative bacteria do not retain the purple dye and are instead red in color.
Yogurt contains mostly lactic acid bacteria, which are Gram-positive bacteria. This means they will stain purple under a Gram stain.
Gram positive are purple. Just remember Positive+Purple. Gram negative are a reddish color from the safranin. After using the crystal violet, the grams iodine acts as a mordant to hold color on cell wall. When using the alcohol, the gram positive will stay purple while the gram negative will become clear. This is due to the outer cell wall of the gram negative specimen (lipopolysaccharide) basically being stripped by the alcohol, so now you have a clear specimen again. When you add the safranin it sticks to the gram negative cell wall, hince the red/pink color.
The color of a gram-negative stain is pink or red. This staining technique is used to differentiate bacteria based on their cell wall composition, with gram-negative bacteria retaining the pink/red color after staining.
S. mitis stains purple and therefore is a gram positive bacteria
Gram positive bacteria appear purple or blue when stained with the Gram stain, while gram negative bacteria appear pink or red. This color difference is due to the thickness of the cell wall and the presence of an outer membrane in gram negative bacteria.
Over destaining can cause the purple color from the gram positive bacteria to be washed away, so when you apply the safrinin the gram positive bacteria will take up a pink color causing gram positive bacteria to appear gram negative.
Gram-negative bacteria have a thinner peptidoglycan layer in their cell wall compared to gram-positive bacteria. They also have an outer membrane containing lipopolysaccharides. When subjected to Gram staining, gram-negative bacteria appear pink or red, while gram-positive bacteria appear purple or blue.
gram positive is purple while gram negative is reddish,gram positive is composed of peptidolycan and also have a little similarities with archean's
Gram-negative bacteria do not retain the purple color in the Gram staining procedure because their cell walls have a thinner layer of peptidoglycan, which does not hold the crystal violet dye as effectively as the thicker peptidoglycan layer in Gram-positive bacteria.