Gram-negative bacteria
![Microscopic image of gram-negative Pseudomonas aeruginosa bacteria (pink-red rods)](/Images/godic/202501/08/Pseudomonas_aeruginosa_Gram3014.jpg")
![Gram-negative cell wall structure](/Images/godic/202501/08/Gram_negative_cell_wall.svg3014.png")
![Gram-positive and -negative bacteria are differentiated chiefly by their cell wall structure](/Images/godic/202501/08/Gram-Cell-wall.svg3014.png")
Gram-negative bacteria are a group of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell membranes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane.