AAT Bioquest

What is the most common example of differential staining?

Posted March 9, 2023


The most common example of differential staining is Gram staining. Gram staining separates bacterial cells into two groups -  gram positive and gram negative. The microbial cells that keep a primary stain color (crystal violet) are stained purple and labeled as gram-positive. The microbial cells that do not keep the crystal violet color are counterstained red with safranin, and are labeled gram-negative. There are several morphological differences between gram-positive and gram-negative cells. Gram positive microbial cells do not have lipid-rich cell walls. In contrast, gram-negative cells have a higher lipid content in cell walls. During decolorization, ethanol may extract the lipids, increasing the permeability of cell walls. Therefore, the crystal violet-iodine complex easily disintegrates. In contrast, gram-positive bacterial cell walls become dehydrated, decreasing the porosity, and the crystal violet-iodine complex is retained.    

Additional resources

Gram Staining

Gram Staining

MycoLight™ Rapid Fluorescence Gram-Positive Bacteria Staining Kit