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 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.