Knowledge Hub

Return to Glossary


Gram-negative bacteria have a cell wall composed of a thin layer of a particular substance (called peptidoglycan) and an outer membrane containing Lipopolysaccharides (LPS, which consists lipid and sugar). They are more resistant to antibiotics. They are named after the Danish bacteriologist, J.M.C. Gram and lose the crystal violet stain (and take the color of the red counterstain) in Gram's method of staining. The Gram-negative bacteria include most of the bacteria normally found in the gastrointestinal tract that can be responsible for multiple diseases. Gram devised a method of staining bacteria using a dye called crystal violet. Gram's method helps distinguish between different types of bacteria the Gram staining characteristics of bacteria are denoted as positive or negative, depending on whether the bacteria take up and retain the crystal violet stain or not. Gram positive bacteria are usually more sensitive to antibiotics.