Which staining technique differentiates bacteria into Gram-positive and Gram-negative?

The Gram staining technique is critical for differentiating bacteria into two major groups: Gram-positive and Gram-negative. This method relies on the structural differences in the bacterial cell wall, which results in different staining properties.

In Gram staining, a crystal violet dye is applied first, which colors all bacteria. This is followed by the application of iodine, which forms a complex with the crystal violet and helps retain it within the cell. Next, a decolorizer, usually alcohol or acetone, is applied. This step is crucial as it acts differently on the two types of bacteria. Gram-positive bacteria, which have a thick peptidoglycan layer, retain the crystal violet and remain purple. In contrast, Gram-negative bacteria, with a thinner peptidoglycan layer surrounded by an outer membrane, lose the primary stain and are subsequently counterstained with safranin, appearing pink.

This distinction not only helps in identifying the type of bacteria present but also has important implications for treatment options, as Gram-positive and Gram-negative bacteria often respond differently to antibiotics. Understanding this technique is fundamental for microbiology and clinical diagnostics.