GRAM STAIN PVP KIT - 4 x 250 mL

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GRAM PVP KIT

PRINCIPLE

The Gram stain was created in 1884 by Christian Gram, and is an essential factor in microbial identifi cation. Although Gram observed what is now known as the “Gram reaction”, he did not recognise the taxonomic value of his technique. The Gram stain makes it possible to diff erentiate bacteria into two groups, according to the colour of the cell after staining. It is a system with two simple, successive stains, separated by a destaining phase. It makes it possible to diff erentiate the bacteria which retain the fi rst colour, and appear blue (Gram-positive) from those that do not retain the colour and are stained pink (Gram-negative). The diff erence is due to the cell wall. The key is peptidoglycan, the material which provides rigidity to the bacterial cell wall. Gram-positive bacteria have a much higher proportion of peptidoglycan than gram-negative bacteria. The cell wall must be intact for correct staining to take place. During the staining, the cell wall of the gram-positive cells is dehydrated by the alcohol of the decolourising agent and it losses permeability. It therefore retains the compound formed by the primary stain (Crystal violet) and the iodine (mordant). By contrast, the gram-negative cells, which have a wall with a higher lipid content, become more permeable when destained with alcohol and lose the primary stain. They are subsequently stained with the counterstain (safranin or fuchsin). This kit diff ers from the classic Gram kit as it contains iodine stabilised with L-polyvinylpyrrolidone, to off er a more stable iodine compound which does not lose its effi cacy as a mordant over time. DIAGNOSTIC USE Gram stain dyes are used to perform the staining of microorganisms, cultures or samples using the Gram diff erential method.

GRAM STAIN PVP KIT - 4 x 250 mL

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