What distinguishes Gram-negative bacteria in laboratory analysis?

Gram-negative bacteria are distinguished in laboratory analysis primarily by their response to the Gram staining procedure, which is a differential staining technique that categorizes bacteria into two groups based on their cell wall structure.

The correct answer indicates that Gram-negative bacteria stain red during this process. This is due to the presence of a thin peptidoglycan layer surrounded by an outer membrane composed of lipopolysaccharides. During the Gram staining procedure, the application of crystal violet dye initially stains all bacterial cells. However, in the case of Gram-negative bacteria, when iodine is applied, this complex can be washed away with alcohol or acetone due to the outer membrane. As a result, when a counterstain such as safranin is applied, Gram-negative bacteria take up this red dye, leading to their distinctive red appearance under a microscope.

In contrast, Gram-positive bacteria possess a thick peptidoglycan layer that retains the crystal violet dye even after the decolorization step, which is why they appear blue. The other options presented do not correctly represent the characteristics of Gram-negative bacteria; they do not stain blue, do not fail to stain entirely, and do not appear green in the Gram staining procedure. Thus, the red staining of Gram-negative