Differences Between Gram Positive and Gram Negative Bacteria

Gram Staining technique is the most important and widely used microbiological differential staining technique. It categorizes bacteria according to their Gram character (Gram positive or Gram negative). Along with their staining characteristics, Gram Positive and Gram Negative bacteria differ from each other in various aspects which are listed below :

S.N. Characteristics Gram Positive Gram Negative
1. Gram Reaction Retain crystal violet dye and stain blue or purple.


Accept safranin and stain pink or red


2. Cell Wall Structure Structure of Gram Positive cell wall :
Structure of Gram Negative cell wall :
3. Cell Wall Thickness Thick (20-80 nm) Thin (8-10 nm)
4. Chemical Composition of Cell Wall Peptidoglycan, Teichoic acid Lipotechoic acid Lipopolysaccharide, Lipoproteins and Peptidoglycans
5. Peptidoglycan Layer Thick (Multilayered) Thin (Single layered)
6. Teichoic Acid in Cell Wall Present Absent
7. Lipopolysaccharide Layer (Outer Layer) Absent Present
8. Lipid Content Absent or lower content of lipids than Gram Negative bacteria Contains higher content of lipids than Gram positive bacteria (due to presence of outer membrane)
9. Porin Proteins Absent Present
10. Flagellar Structure 2 rings in basal body 4 rings in basal body
11. Periplasmic Space Absent Present
12. Mesosome More prominent Less prominent
13. Ratio of RNA:DNA 8:1 Almost 1
14. Toxins Produced Primarily Exotoxins Endotoxins and Exotoxins (Primarily Endotoxins)
15. Resistance to Physical Disruption High Low
16. Cell Wall Disruption by Lysozyme High.
After digestion of peptidoglycan layer, Gram +ve bacteria become Protoplast.
After digestion of peptidoglycan layer, Gram -ve bacteria become Spheroplast.
17. Susceptibility to Penicilin and Sulphonamide High Low
18. Susceptibility to Streptomycin, Chloramphenicol and Tetracycline Low High
19. Inhibition by Basic Dyes High Low
20. Susceptibility to ionic detergents High Low
21. Resistance to Sodium Azide High Low
22. Resistance to Drying High Low
23. Isoelectric Range pH 2.5-4.0 4.5-5.5
24. Nutritional Requirements Relatively Complex Relatively Simple
25. Rendering They can rendered Gram -ve by increasing acidity They can rendered Gram +ve by increasing alkalinity
26. Morphology Usually cocci or spore forming rods (exception : Lactobacillus and Corynebacterium) Usually non-spore forming rods (Exception : Neisseria)
27. Examples
  • Staphylococcus
  • Streptococcus
  • Bacillus
  • Clostridium
  • Nocardia
  • Propionibacterium
  • Enterococcus
  • Corynebacterium
  • Listeria
  • Lactobacillus
  • Gardnerella
  • Escherichia
  • Salmonella
  • Klebsiella
  • Proteus
  • Helicobacter
  • Hemophilus
  • Vibrio
  • Shigella
  • Neisseria
  • Enterobacter
  • Pseudomonas
Differences Between Gram Positive and Gram Negative Bacteria
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