Difference Between Gram Positive And Gram Negative Bacteria

What Is Bacteria

Bacteria is a single-celled microorganism which can exist either as an independent, in other words freely living organism. That can not be seen by unaided (Naked) eyes. Bacteria belong to the prokaryotic group, bacteria is measured in micrometer. In this article, we will study the difference between gram-positive and gram-negative bacteria.

What Are Gram-Positive Bacteria?

Gram-positive bacteria retain the color of crystal violet. Gram-positive microscopic bacteria are made up of a thick layer of peptidoglycan. There are a few instances of gram-positive bacteria.
  1. Streptococcus
  2. Staphylococcus
  3. Clostridium
  4. Anthrax
  5. Mycobacterium Tuberculosis
  6. Enterococcus
  7. Lactobacillus
  8. Gardnerella Vaginallus

What Are Gram-Negative Bacteria?

Gram-negative microscopic organisms did not retain the color of crystal violet and gram-negative microscopic organisms made with a thin layer of peptidoglycan. We can use gram staining for differentiating between gram-positive and gram-negative microscopic bacteria. There are a few instances of gram-negative microscopic organisms.
  1. Escherichia Coli
  2. Pseudomonas
  3. Acenactobacter
  4. Klebsiella Pneumonia
  5. Salmonella
  6. Neisseria
  7. Vibrio
  8. Shigella

Difference Between Cell Wall Of Gram-Positive And Gram-Negative Microscopic Bacteria

 Character  Gram-Positive   Gram-Negative 
  Thickness   Thicker      Thinner
 Absent  Present
  Lipids  Absent  Present 
 Present   Absent
  Peptidoglycan   16-18 nm  2-3 nm 

What Is Cell Wall Of Bacteria?

The cell wall of gram-positive and gram-negative microscopic bacteria is a though and rigid structure surrounding the bacterium like a shell. The cell call of gram-positive and gram-negative microscopic organisms thicker size is 10-25 nanometer, the weight of microscopic bacteria is about 20-25% of the dry weight of the cell.
The rigid part of the microscopic bacteria cell wall is peptidoglycan, The cell wall of gram-positive microscopic organisms has simpler chemical nature than those of gram-negative microscopic organisms.

Function Of Cell Wall Of Bacteria

  • Account for the shape of the cell
  • Provide protection to the cell against the osmotic damage.
  • Confers rigidity upon microscopic organisms
  • Help in cell division takes a part of cell division
  • It possesses a target site for antibiotics, lysozyme, and bacteriophages.

Gram-Positive Cell Wall

In gram-positive microscopic organisms, there are few components that are present.
  • Peptidoglycan:- In the gram-positive microscopic organisms, the peptidoglycan layer is thicker than that of the gram-negative microscopic organisms.
  • Teichoic Acid:- In the gram-positive microscopic organisms cell wall of bacteria contain more much amount of teichoic acid in gram-positive organisms and in gram-negative organisms teichoic acid is absent.

Gram-Negative Cell Wall

  • Lipoprotein
  • Outer membrane
  • Lipopolysaccharide: It constitutes the endotoxin of gram-negative bacteria. This layer consists of lipid A to which attached a polysaccharide. The polysaccharides determine a major surface antigen, the O antigen. The toxicity of bacteria is associated with wth lipid A.
  • The periplasmic space 
  • Peptidoglycan

Study Of Bacteria

1. Unstaid Preparation

Unstained preparation also is known as wet preparation in the study of bacteria, unstained, or wet examination is mostly used for motility and demonstration of microscopic organisms.

2. Stained Preparation

The structure of microscopic bacteria can not be seen under a light microscope due to lack of a contract, then we have only one way to microscope the organism with the use of staining methods to produce color constant. The smart of bacteria is made from the bacterial culture, first of all, we can fix the smear with heat and flaming the slide from underneath.
We can use heat first because heat is used to kill the contaminated particles and fix the smear om the slide due to the coagulation of bacterial proteins.and the fixed the smart is stained by the different types of standing technique.

Detection Of Gram-Positive and Gram-Negative Organisms

Gram stain is used to differentiate gram-positive and gram-negative microscopic organisms. Gram stain is most widely used in the study of bacterial structure and bacteriology. 
The gram stain technique is first and originally devised by the histologist Christian gram in 1884. in this time there are different types of modifications in the technique of gram staining.

Method Of Gram Staining:-

  1. First of all, you can heat the smear of the specimen or bacterial culture.
  2. Then, pour the crystal violet for one minute. You can also use pararosanilne dyes such as gentian violet or methyl violet may also be used in place of crystal violet.
  3. Wash the smear with tap water.
  4. After pouring crystal violet you can pour grams iodine, dilute solution of iodine put over the slide for one minute. 
  5. Wash the smear with tap water.
  6. After pouring grams iodine you can pour the decolorize with acetone for 10-30 seconds. Alcohol can be substituted for acetone.
  7. Wash the smear with tap water.
  8. After pouring acetone you can pour counterstain with a dye safranin for 30 seconds. Diluted carbol fuchsin or neutral red may also be used as counterstain. 
  9. Then wash with tap water.
  10. Dry the smear and go for the microscopy 

Observation Of Gram Staining

In observation of gram staining, we can see the difference between gram-positive and gram-negative microscopic organisms,


  • Resist decolorization and retain the color of the primary stain.
  • Gram-positive microscopic organisms paper in violent color.
  • Gram-negative microscopic bacteria appear in red color.
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