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Difference Between Gram Positive And Gram-Negative Cell Wall


Bacteria are present all around us, contributing to different environmental functions. They are dispersed in air, present on surfaces, on our skin, and inside the body. Some are known as “good bacteria,” and some are “bad bacteria.” Besides good and bad bacteria, they are classified as Gram-positive and gram-negative bacteria due to differences in their characteristics. They both react to stains in different ways and comprise particular organisms. 

Let’s tell you the differences between Gram-Positive and Gram-Negative Cell Wall and why they are named so.

Comparison Table

Thickness20 to 80 nm8 to 10 nm
StainingPurple colorPink color
Teichoic acidsPresent Absent
Lipid contentMinimal to absentHigh 
Outer membraneAbsentPresent
Drying resistanceHigh resistanceLow resistance
Antibiotic resistanceLess resistantHighly resistant

What are Bacteria?

The simplest example of bacteria is “unicellular microorganisms found everywhere, and can only be seen under a microscope. They are made of prokaryotic cells and are thus called prokaryotic organisms. Prokaryotes, like bacteria, lack double-membrane-bound structures, including the nucleus and mitochondria.

There are about 30,000 types of bacteria known to researchers, and studies show that Earth has around a trillion species of microorganisms, out of which 99.999% are still undiscovered. 

Structure of Bacteria

Before we talk about the difference between gram-positive and gram-negative cell walls, it is important to understand the basic structure of the bacterial cell. A bacterial prokaryotic cell consists of the basic structure and lacks a nucleus, mitochondria, endoplasmic reticulum, lysosomes, centrosomes, etc.

The structure of bacteria has:

Types of Bacteria

Bacteria are divided into multiple categories according to their characteristics. One of the most important classifications is gram-positive and gram-negative. Scientists and healthcare professionals identify these bacteria per their staining ability. This classification enables researchers to discover the reason behind bacterial infections, derive antibiotics, and offer appropriate treatment to the patients.

  • Gram-negative
  • Gram-positive

What are Gram-Positive Bacteria?

Gram-positive are those which give a “positive” result when stained. They retain the crystal violet stain of ethanol and iodine when introduced to the bacterial cells. The reason for taking the color of the dye is a slight change in their cell wall compared to gram-negative. Their cell wall has a thick structure with many peptidoglycans, phosphate, and teichoic acid layers. Two types of Teichoic acids are found in the cell wall of these bacteria; teichoic wall acid and lipoteichoic acid.

Examples of gram-positive bacteria include staphylococci and pneumococci.


What are Gram-Negative Bacteria?

Gram-negative bacteria get their name from the inability to absorb the violet color of the stain. However, it does not mean they do not take up any color. Instead, they retain the hue of the red dye used as counterstain. Again, the absorbance of the color is dependent on the composition of the cell wall. The gram-negative cell wall does not have a thick peptidoglycan layer; instead of a thin one. Lipoproteins in the cell wall have peptidoglycans attached to them. The periplasm between the payers contains degrading enzymes and proteins

The chemical used to stain gram-negative cell walls is Safranin, often known as the counterstain. It can be washed with an alcohol wash to remove the color. Gram-negative bacteria include H. Pylori and E. Coli. You can observe these bacteria in a slight pink color under the compound microscope.


Similarities Between Gram-Positive and Gram-Negative Cell Wall

  • Cell walls are present in both kinds of bacteria.
  • They both contain peptidoglycan in their composition.
  • They can be stained using particular dyes to be observed under the compound or electron microscope.
  • They contribute to providing structural support to the bacteria.

Difference Between Gram Positive and Gram-negative Cell Wall



Gram-positive bacteria are those bacteria that have a gram-positive cell wall and obtain a color through staining.


Whereas gram-negative bacteria have a gram-negative cell wall and obtain a color through counterstain.



The thickness of the gram-positive bacterial cell wall is between 20 to 80 nanometers.


In comparison, a gram-negative cell wall has a thickness of 8 to 10 nanometers.



They obtain a beautiful crystal violet color on staining.


On the other hand, you observe a pinkish hue on gram-negative bacteria on staining with a counterstain. 



They have a thick peptidoglycan layer made of multiple stacked layers.


Alternatively, the peptidoglycan layer in gram-negative bacteria is thin compared to gram-positive bacteria.

Teichoic Acids


Gram-positive bacteria cell walls have teichoic acids, including lipoteichoic and teichoic wall acid.


Conversely, gram-negative bacterial cell walls do not have teichoic acids.

Lipid Content


The lipid content in gram-positive cell walls is very low to absent.


Although gram-negative bacteria have a high lipid content in their cell wall.

Outer Membrane


No outer membrane is present in gram-positive bacteria.


Yet, gram-negative bacteria have an outer membrane.



Gram-positive bacteria do not have periplasm due to the absence of an outer wall.


At the same time, gram-negative bacteria contain periplasm between the layers.

Drying Resistance


Gram-positive bacteria have a high resistance to drying.


However, gram-negative bacteria are not as resistant to drying as gram-positive.

Antibiotic Resistance


Gram-positive bacteria are less resistant to antibiotics.


In contrast, gram-negative bacteria have a higher resistance to antibiotics.



What are the characteristics of gram-positive bacteria?

Gram-positive bacteria have all the structures present in a prokaryotic cell. They lack a nucleus and mitochondria and have a thick cell wall made of multiple layers of peptidoglycan. Their cell wall is up to 80 mm in thickness. They do not have an outer layer and retain the crystal violet stain.

What antibiotics cover gram-positive and gram-negative?

Cloxacillin and penicillin are typically used for gram-positive bacteria, and cephalosporins treat gram-negative organisms. Whereas penicillin and erythromycin are called broad-spectrum antibiotics and are effective against both kinds of bacteria.

What is the difference between gram-positive and gram-negative bacteria staining?

Gram-positive and gram-negative bacteria have distinct cell walls that take different kinds of stains. Gram-positive ones take up a violet stain while gram-negative ones have a pink stain.

Which is more harmful- gram-positive bacteria or gram-negative bacteria?

Gram-negative bacteria are more harmful compared to gram-positive bacteria and are more resistant to antibiotics because of the presence of a slimy outer layer.

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