388K views · 7.7K reactions | The Gram Stain is a microbiology technique used to classify bacteria into two large groups: Gram-positive (purple) and Gram-negative (pink), based on the structure of their cell walls. This technique was developed approximately 80 years before the invention of the electron microscope allowed scientists to visually confirm the underlying cell wall differences that cause the stain variation. | Ribosome Studio | Facebook