Difference between Gram-positive and Gram-negative bacteria

gram-positive and gram-negative bacteria


Microorganisms are categorized under bacteria, viruses, fungi, and mycoplasma. Some of the microorganisms are disease-causing some are saprophytes or some are heterotopic in nature. Bacteria are cosmopolitan, unicellular, rigid cell walled, prokaryotic microorganisms. They are simple in structure causes diseases in plants and animals. The following article is about the gram-positive and gram-negative bacteria and its features.

Characteristic features of bacteria

  1. Bacteria are found almost everywhere, they are simple, unicellular, and primitive organisms.
  2. The bacteria are autotropic, parasitic, saprophytic, and symbiotic in nature.
  3. Bacteria are prokaryotic in nature and do not have a well developed genetic system.
  4. It lacks cellulose but has a rigid cell wall composed of mucopeptide.
  5. Bacteria are both motile and nonmotile in nature.
  6. Sexual reproduction is commonly absent in bacteria. Genetic recombination is one of the methods that take place in some bacteria.
  7. Reproduction takes place by fission or budding.
  8. Asexual reproduction by spores, conidia, and endospores.

Staining of Bacteria

On the basis of the staining process, bacterias are divided into two types

  1. Gram-Positive (Gram ‘+’)
  2. Gram-Negative (Gra, ‘-’)

How to do Gram staining

Gram staining was first done by Danish bacteriologist Christian Gram. The easy steps of Gram staining are as follows1.

Take a clear glass slide and make a thin smear of bacteria.  After that stain with basic stain-crystal violet.

Observation: Both the gram-positive and gram-negative bacteria will get stain having purple-blue in color.

2. Stain the bacteria with a Gram iodine solution.

Observation: crystal violet complex forms that maintain the stain.

3. Decolorize the stain with decolorizer (ethyl alcohol and acetone).

Observation: gram-positive bacteria saw violet and gram-negative bacteria are colorless under a microscope.

Note: This step is known as a differential step.

4. Basic counter stain known as safranin is applied on the slide which affects the gram-negative bacteria that appeared as red or pink.

Difference between Gram-positive and Gram-negative Bacteria



The appearance of cell wall under a microscopeThe cell wall of gram-positive bacteria appears homogenous.The cell wall appears three-layered.
The thickness of the cell wallIt has a thick cell wall (up to 150-200 A0)It has a thin cell wall (75-120 A0).
Composition of cell wallThe gram-positive bacterial cell wall is composed of 80% mucopeptide and rest is polysaccharides.Less mucopeptide compared to gram-positive bacteria (3-12%)
Lipid quantityComparatively less lipid (1-4%)High lipid as compared to gram-positive bacteria (11-22%).
The resistivity of the cell wallThe wall is resistant to alkalies and insoluble in 1% KOH solution.It is sensitive to alkalies and is soluble in 1% KOH solution.
PathogenicityThe gram-positive bacteria are spore-producing and only a few are pathogenicMost of the gram-negative bacteria are pathogenic and are polarly flagellate.
MesosomesMore distinctLess distinct
Teichoic acidIt is present and the amount of teichoic acid  is 5-10%Teichoic acid is absent in the cell wall.
The rigidity of the cell wallMore rigidElastic in nature
Resistivity to antibioticsLess resistance to antibioticsHighly resistive to antibiotics
Nutritional requirementsComplexSimple

Source: Advances in Microbiology: P C Trivedi

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