Which feature distinguishes Gram negative bacteria?

The distinguishing feature of Gram-negative bacteria is that they possess a thin peptidoglycan layer in their cell wall. This thin layer is situated between the inner cytoplasmic membrane and the outer membrane, which is characteristic of Gram-negative organisms. The outer membrane contains lipopolysaccharide (LPS), which can trigger strong immune responses in humans and animals. This structural composition is crucial as it affects the bacteria's reaction to Gram staining, leading to a pink or red coloration under the microscope after the staining procedure, in contrast to the thicker peptidoglycan layer found in Gram-positive bacteria, which retains the crystal violet stain.

In terms of overall context, while Gram-positive bacteria are characterized by their thick peptidoglycan layer that retains the primary stain during Gram staining, Gram-negative bacteria's thin peptidoglycan layer and the presence of the outer membrane are critical for their identification and understanding their pathogenic mechanisms. The absence of spores and the presence of an outer membrane are also key recognizable features when classifying bacteria, but they do not specifically point to the distinction of Gram-negative bacteria as clearly as the thin peptidoglycan layer does.