What type of stain is used to distinguish different types of bacteria?

The Gram stain is a fundamental technique used in microbiology to classify bacteria into two groups: Gram-positive and Gram-negative. This distinction is based on the structural differences in the bacterial cell wall. Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet dye used in the staining process, causing them to appear purple under a microscope. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane that does not retain the dye, resulting in them appearing pink after being counterstained with safranin.

The Gram stain is essential for guiding the selection of appropriate antibiotics for treatment, as the response of bacteria to certain drugs can differ significantly depending on whether they are Gram-positive or Gram-negative. While other staining methods, such as the acid-fast stain for mycobacteria or methylene blue for general observation, serve specific purposes, the Gram stain remains a primary method for rapidly differentiating between bacterial types in clinical and laboratory settings.