Difference Between Gram-Positive and Gram-Negative Bacteria

Bacteria are single-cell, prokaryotic microorganisms. While studying bacteria, it is important to classify them for information management purpose. There are several methods available to categories bacteria. These include simple methods like classification on the basis of cell shape, e.g. bacilli and cocci. We can also classify bacteria as per their growth in high or low oxygen environments. Gram staining is another method to classify bacteria on the basis of how bacteria retain the Gram stain. Hans Christian Gram, a danish biologist, developed the Gram stain. The Gram staining method also make bacteria more visible under a microscope. A bacteria can either be Gram-Positive or Gram-Negative.

Major Differences Between Gram-Positive and Gram-Negative Bacteria

Differences Between Gram-Positive and Gram-Negative Bacteria
Basis of Comparison Gram-Positive Bacteria Gram-Negative Bacteria
Diagrams gram positive bacteria gram negative bacteria
Gram Staining Stain blue or purple Stain pink or red
Dye Retention
Retain crystal violet dye Retain safranin dye
Cell Wall Single-layered and smooth Double-layered and wavy
Thickness of Cell Wall Thick (20-80 nm) Thin (8-10 nm)
Peptidoglycan Layer Thick  and can be multilayered Thin and often single-layered
Rigidity Rigid Relatively more elastic
Outer Membrane Absent Present
Periplasmic Space Absent Present
Lipopolysaccharide Content Very low High
Lipid Content Low 20 to 30%
Flagellar Structure Two rings in basal body Four rings in basal body
Magnetosomes Usually absent Sometimes present
Morphology Usually cocci or spore forming rods Non-spore forming rods
Toxin Production Exotoxins Endotoxins or Exotoxins
Pathogens Only a few pathogenic bacteria are Gram-Positive Most pathogenic bacteria are Gram-Negative
Inhibition by Basic Dyes High Low
Rendering Can render Gram-Negative with increasing acidity Can render Gram-Positive with increasing alkalinity
Examples Staphylococcus, Streptococcus, Bacillus, Clostridium, Enterococcus Escherichia, Salmonella, Klebsiella, Helicobacter, Pseudomonas

Gram-Negative bacteria offer more resistance to antibodies because their cell-wall is impenetrable.