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Differential Stain

allow to detect differences between organisms or differences between parts of the same organism

gram stain

most commonly used differential stain in bacteriology

gram stain

differential stain in which a decolorization step occurs between the application of two basic stains

crystal violet

primary stain




to enhance crystal violate staining by forming a crystal-violet iodine complex

forms a crystal-violet iodine complex to enhance the crystal violet stain

what does iodine do after stained with crystal violet


what is the most critical step in differential stain

gram negative cells

these cells are decolorized by the solution (alcohol or acetone) whereas gram positive are not

gram negative cells

__________________ can be colorized by the counterstain


what is the counterstain

gram negatives have higher lipid content because of the outer membrane and a thinner peptidoglycan layer than gram positive cell walls

gram negative cells are able to resist decolorization due to


_________ in the decolorizer extracts the lipid making the gram negative wall more porous and incapable of retaining the crystal violet iodine complex thereby decolorizing it

thick peptidoglycan wall

the reason why gram positive cells are less susceptible to decolorization is because of


leaving the alcohol on too long and get reddish gram positive cells


produce purple gram negative cells


____ of the culture affects gram stain consistency

older gram positives

may lose their ability to resist decolorization and give an artificial gram - result

cell morphology, size and arrangement

gram stain allows

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