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Difference between Gram-positive and Gram-negative Bacteria

Difference between Gram-positive and Gram-negative Bacteria

Gram-Positive Vs. Gram-Negative Bacteria

What is the Difference between Gram-positive and Gram-negative Bacteria?

Danish scientist Hans Christian Gram designed a method that allowed him to differentiate two types of bacteria based on their cell walls (gram-positive bacteria and gram-negative bacteria).

Because of their structural differences, these two types of bacteria do not respond the same way to the antibodies, for that reason,

It is important that we know the difference between one and the other; so that we can better understand what utility each type can have or what it might cause.

Difference between Gram-positive and Gram-negative Bacteria

If you have doubts about the difference between gram-positive and gram-negative, continue reading.

Gram-positive Bacteria

They are those that are characterized to maintain a purple or blue dye once the test of staining or staining of Gram is applied to them.

This is due to the structure of your cell wall. The gram-positive does not have an outer cell membrane;

instead, they contain a great amount of peptidoglycan; which is responsible for maintaining the violet coloration.

Many gram-positive bacteria are non-pathogenic, i.e. they do not cause disease;

Instead, they are also part of the human commensal microbiomes found in the mouth, skin, intestine, and respiratory tract.

They are also a necessary ingredient in the production of some foods; as is the case of Swiss cheese.

Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane.

Gram-positive bacteria cause serious problems and are the focus of disease control.

Gram-negative Bacteria

On the other hand, when applied to the aforementioned test, the gram-negative bacteria acquire a red or pink coloration.

Unlike gram-positive, they do have an outer cell membrane.

Between 90-95% of gram-negative bacteria are pathogens for humans.

Additionally, they are resistant to antibiotics or develop resistance to them more quickly than gram-positive bacteria.

Gram negative bacteria have a thin peptidoglycan layer and an outer lipid membrane.

Gram-negative bacteria develop dangerous resistance. Thus, classified by the CDC as a more serious threat.


Finally, not all bacteria can be classified by the Gram test.

Parameter Gram-Positive bacteria Gram-Negative bacteria
Cell Wall A single-layered, smooth cell wall  A double-layered, wavy cell-wall
The Thickness of Cell Wall The thickness of the cell wall is 20 to 80 nanometres The thickness of the cell wall is 8 to 10 nanometres
Peptidoglycan Layer It is a thick layer/ also can be multilayered It is a thin layer/ often single-layered.
Teichoic acids Presence of teichoic acids Absence of teichoic acids
Outer membrane There is no outer membrane presence. The outer membrane is mostly present
Porins No Porins Present Appears on outer Membrane
Mesosome Prominence is more prominence is less.
Morphology Spore-forming rods or Cocci No spore-forming rods.
Flagella Structure 2 rings in basal body 4 rings in basal body
Lipid content Quiet Low lipid content 20-30% lipid content
Lipopolysaccharide Not Present Present
Toxin creation Only Exotoxins Exotoxins or Endotoxins both
Resistant level Less Resistant More resistant
Illustrations Streptococcus, Staphylococcus Salmonella, Escherichia
Gram Staining  Retains the crystal violet color even washing with alcohol or acetone and appears purple-colored under microscopic examination after gram staining.
Do not retain the stain color even washing with alcohol or acetone and appear as pink-colored under microscopic examination after gram staining.

Comparison table

For Further Reading

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