What is the primary method used to differentiate bacteria into Gram-positive and Gram-negative?

The primary method used to differentiate bacteria into Gram-positive and Gram-negative is Gram staining. This technique involves a multi-step process that uses specific dyes and reagents to color the bacterial cells.

In Gram staining, the bacteria are first treated with a crystal violet dye that gives all cells a purple color. This is followed by the application of iodine, which acts as a mordant and helps to fix the dye within the cells. After that, a decolorizer, typically alcohol or acetone, is applied. This step is crucial because it distinguishes between the two types of bacteria based on their cell wall structure. Gram-positive bacteria, which have a thick peptidoglycan layer, retain the crystal violet stain and remain purple, while Gram-negative bacteria, which possess a thinner peptidoglycan layer and an outer membrane, do not retain the stain and will take up the counterstain (usually safranin), appearing pink.

This fundamental staining technique is essential in microbiology as it not only aids in bacterial identification but also gives insight into the bacterial cell wall's structural characteristics, which can have implications for treatment efficacy and susceptibility to antibiotics.