Gram technique works, but not the way scientists thought
From left: Riraq25/Wikimedia (CC-BY-SA-3.0); CDC
With delicate hues of purple and pink, a lab technique called gram staining has reliably characterized bacteria for more than a century. Yet many scientists are mistaken about why the vivid method works, new research finds.
Contrary to standard scientific texts, the purple dye called crystal violet, a main ingredient in gram staining, does not actually enter bacterial cells, researchers report April 27 in ACS Chemical Biology. Instead, the dye gets trapped in a tight package of sugar-filled polymers, called peptidoglycan, which envelops bacterial cells. The thickness and integrity of the sweet bacterial armor determines whether crystal violet leaves a cell purple or not. That royal shade, or lack of it, reveals a cell’s type of outer structure.
Published by Hans Christian Gram in 1884, gram staining distinguishes gram-positive bacteria (purple) from gram-negative bacteria (pink