text: The positives can be stained, the others can't. The staining possibility is an advantage for further research under a microscope. There is even more to it because Gram-positive bacteria belong to a separate phylum different from the Gram negatives.  The stain becomes possible by a high amount of peptidoglycan in the cell wall, which typically, but not always lacks the secondary membrane and lipopolysaccharide layer found in Gram-negative bacteria