Schematic diagram of bacterial cell walls Grant rram Peptidoglycan 一 Peptidoglycan Membrane Membrane I Periplasm Lipopolysaccharide and protein Bacteria can be divided into two major groups, called gram-positive and gram-negative. The original distinction between gram-positive and gram-negative was based on a special staining procedure, the Gram stainGram+ Gram - Schematic diagram of bacterial cell walls Bacteria can be divided into two major groups, called gram-positive and gram-negative. The original distinction between gram-positive and gram-negative was based on a special staining procedure, the Gram stain