Why is Gram-Staining Important?

Gram-staining separates bacteria into gram-positive and gram-negative groups, based on the microorganisms' abilities to retain the dye crystal violet during decolorization with alcohol.  The color difference between the two reflects differences in the outer surface structure of the microorganisms. 

To Gram-Stain:

Interpreting the results:

So how do you tell which bacteria you observe under the microscope are gram-negative and which are gram positive? Gram-negative bacteria have a pink color because they lost the purple color of the crystal violet during the decoloriztion process and were left with only the pink of the safranin. Gram-positive bacteria have a purple color since they retained the dye from the crystal violet, even after decolorization.


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