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'''Gram negative bacteria stain pink''' following a Gram stain, whereas Gram positive bacteria stain purple.

'''Gram negative bacteria stain pink''' following a Gram stain, whereas Gram positive bacteria stain purple.

==Gram Stain==

==Gram Stain==

This is the most widely used differential stain. The primary stain (crystal violet) is applied. This is then washed away and a '''mordant''' (iodine solution) is applied to complex the crystal violet to the bacterial cell. This is removed and a '''decolourising agent''', usually acetone, is aplied. This '''removes the purple stain''' only from the Gram negative bacteria, while Gram positive organisms retain it. The unstained Gram negatives are then visualised with a '''red counterstain''', usually Carbol Fuchsin, which will not alter the purple appearance of Gram positives.

This is the most widely used differential stain. The primary stain (crystal violet) is applied. This is then washed away and a '''mordant''' (iodine solution) is applied to complex the crystal violet to the bacterial cell. This is removed and a '''decolourising agent''', usually acetone, is applied. This '''removes the purple stain''' only from the Gram negative bacteria, while Gram positive organisms retain it. The unstained Gram negatives are then visualised with a '''red counterstain''', usually Carbol Fuchsin, which will not alter the purple appearance of Gram positives.

Dead bacteria, cells and organic debris will stain pink. In older cultures of Gram positive bacteria there are likely to be dead cells which stain pink. Since Gram negative bacteria do not give false positive reaction it is usually safe to assume that bacteria giving a doubtful reaction are Gram positive.

Dead bacteria, cells and organic debris will stain pink. In older cultures of Gram positive bacteria there are likely to be dead cells which stain pink. Since Gram negative bacteria do not give false positive reaction it is usually safe to assume that bacteria giving a doubtful reaction are Gram positive.

See a list of the [[:Category:Gram negative bacteria|Gram negative bacteria]].

See a list of the [[:Category:Gram negative bacteria|Gram negative bacteria]].

==References==

==References==

Black, J. (2008) '''Microbiology: principles and explorations''' ''John Wiley and Sons''

Black, J. (2008) '''Microbiology: principles and explorations''' ''John Wiley and Sons''

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[[Category:Gram negative bacteria|A]]

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