Who invented the Gram staining technique?

Hans Christian Gram invented the Gram staining technique. The Danish bacteriologist developed the method in Berlin in 1884 while working with Carl Friedländer and examining bacteria in lung tissue. Gram’s original goal was to make bacteria more visible under a microscope, not to create the modern two-group classification system associated with the test.

The procedure uses crystal violet as a primary stain, iodine to help fix that dye, alcohol or another decolorizer, and a counterstain such as safranin. Bacteria with thick peptidoglycan cell walls retain the violet dye and are called Gram-positive. Those with thinner peptidoglycan layers lose the violet during decolorization and take up the counterstain, appearing pink or red as Gram-negative bacteria.

Gram staining remains one of microbiology’s first identification steps because it quickly narrows the possibilities when an infection is suspected. A common mix-up is assuming the technique identifies every bacterium perfectly; some organisms are gram-variable or gram-indeterminate, and staining results must be interpreted alongside culture, microscopy, and other tests.