Differences Between Gram Positive and Gram Negative Bacteria

Bacteria are a huge group of single-celled microscopic organisms categorized as prokaryotic cells (lack true nucleus). Their inner structure is simple composing mainly of capsule, cellular wall, cytoplasm, ribosomes, DNA, pili, and flagellum. Bacteria can either be a gram-positive or gram-negative, and to find it out, a gram-staining technique has to be used.
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.

Gram-Positive

Accept safranin and stain pink or red

Gram-Negative

2. Cell Wall Structure Structure of Gram Positive cell wall :
gram-positive-cell-wall
Structure of Gram Negative cell wall :
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.
Low.
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

 

Frequently Asked Questions

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Some of the common gram-positive bacteria you will encounter in the healthcare setting as they are the leading causes of clinical infections are:

  • Staphylococcus
  • Streptococcus
  • Bacillus
  • Clostridium
  • Nocardia
  • Propionibacterium
  • Enterococcus
  • Corynebacterium
  • Listeria
  • Lactobacillus
  • Gardnerella

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Of the two, gram-negative bacteria are more harmful as their outer membranes are protected by a slim layer hiding antigens present in the cell. If the infection is caused by gram-negative bacteria, it would require a strong dose of antibiotics and strict compliance to the course of treatment to thoroughly get rid of the harmful bacteria.

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Yes. Gram-positive bacteria’s cell wall can easily absorb antibacterial cleaning products and antibiotics because of their outer peptidoglycan layer.

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Some of the infections caused by gram-positive bacteria include the following:

  • Urinary tract infection
  • Tuberculosis
  • Diphtheria

 

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Some of the infections caused by gram-negative bacteria are:

  • Bloodstream infections
  • Pneumonia
  • Meningitis

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No. It is a rod-shaped gram-negative bacterium.

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Gram-negative bacteria are more difficult to destroy than gram-positive. The most effective approach is to use a combination therapy, especially antibiotics with dual-mechanism action.

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Yes. It needs a strong dose of antibiotic and combination treatment to thoroughly destroy the pathogen.

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4 Responses to Differences Between Gram Positive and Gram Negative Bacteria

  1. akshay June 12, 2016 at 8:13 am #

    figure of gram negative and positive bacteria is given incorrect.please have a look…

  2. asad October 11, 2016 at 9:17 pm #

    Figure gram positive and negative walls is just confusing please take a look.

  3. monkeybaby February 24, 2017 at 7:29 pm #

    The pics for gram neg and gram pos cell walls need to be swapped! Just thought I’d let you know. 😉

  4. Nadjo Deen March 21, 2017 at 10:00 pm #

    where can I get ur pdf filed to download ?

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