Difference Between Gram Positive and Gram Negative Bacteria


Gram positive and gram negative staining

Gram Positive Bacteria Vs Gram Negative Bacteria
(Similarities and Differences Between Gram Positive and Gram Negative Bacteria)

What is Grams staining?

Christian Gram, a Danish Physician in 1884 developed a staining technique to distinguish two types of bacteria. The two categories of bacteria based on gram staining are Gram positive bacteria and Gram negative bacteria. Bacteria are first stained with crystal violet or gentian violet. All bacterial cells will stain blue or purple colour with crystal violet solution. Then the bacterial cells are treated with iodine solution (Lugol’s iodine) solution and washed with alcohol (de-staining solution).  Those bacteria which retain the blue or purple colour of crystal violet are called Gram positive bacteria and those bacteria which loose the colour of crystal violet after washing with de-staining solution is called Gram Negative bacteria. Gram negative bacteria are later stained with safranin or fuchsin for observation under microscope. Gram negative bacteria after safranin or fuchsin staining will appear red or pink colour. Gram staining differentiates bacteria by the chemical and physical properties of their cell walls by detecting the properties of peptidoglycan. Gram staining method is useful in differentiating majority of bacterial species into two broad categories. Even though all bacterial species cannot be differentiated based on gram staining technique, this method has immense application in clinical diagnostics and biological researches.

Similarities between Gram Positive and Gram Negative Bacteria

Ø  Both are bacterial cells

Ø  Both groups are prokaryotic

Ø  Both lack membrane bounded organelles

Ø  Both groups have covalently closed circular DNA as the genetic material

Ø  Both groups contain extra-chromosomal genetic materials (plasmids)

Gram stain 01

Gram Positive (blue) and Gram Negative (Pink) Bacteria (source wikipedia)

Ø  Both groups possess capsule

Ø  In both groups, cell wall is made up of peptidoglycan

Ø  In both groups, cytoplasm is surrounded by lipid bilayer with many membrane spanning proteins

Ø  Both gram-positive and gram-negative bacteria commonly have a surface layer called an S-layer

Ø  Both groups of bacteria undergo genetic recombination through transformation, transduction and conjugation

Ø  Both groups undergo binary fission as a mode of asexual reproduction

Ø  Both groups contain many flagellated and non-flagellated species

Ø  Both gram positive and gram negative bacteria are inhibited by antibiotics (their sensitivity varies)

Ø  Both groups includes flagellated (motile) and non-flagellated (non-motile) forms


Learn more…

Difference between Prokaryotes and Eukaryotes

Difference between Archaebacteria, Bacteria and Eukaryote

Difference between Prokaryotic and Eukaryotic Transcription

Difference between Prokaryotic and Eukaryotic Translation


Difference between Gram Positive Bacteria and Gram Negative Bacteria

Sl. No.Gram Positive BacteriaGram Negative Bacteria
1Appears as dark violet or purple coloured under microscope after Gram stainingAppears as pink or red coloured after Gram staining
2Retain the colour of crystal violet after washing with alcohol (de-staining solution)Colour of crystal violet will not be retained after washing with de-staining solution

Gram Stain Anthrax.jpg

Pseudomonas aeruginosa Gram.jpg

3Examples: Bacillus subtilis, Streptococcus, Lactobacillus, Leuconostoc, ClostridiumExamples: Escherichia coli, Rhizobium, Vibrio, Acetobacter
4Cell wall single layered, straight and evenCell wall two layered and uneven (wavy)
5Cell wall is very rigid and less elasticCell wall is less rigid and more elastic
6The rigidity of cell wall is due to the high proportion of peptidoglycans (80%)The elasticity of cell wall is due to the less amount of peptidoglycan (2 – 12 %)
7Thickness of cell wall varies from 15- 20 nm, sometimes up to 80 nmThickness of cell wall varies from 7.5 to 12 nm
8Muramic acid content of cell wall is more, 16 – 20% of dry weightMuramic content of cellwall is less, 2 – 5% of dry weight
Gram Positive Vs Gram Negative BacteriaBacterial Cell wall Structure
9Cell wall is resistant to alkalis and insoluble in 1% KOH solutionCell wall is sensitive to alkalis and soluble in 1% KOH solution
10Cell is highly resistant to physical disruptionsCell is highly susceptible to physical disruptions
11S-layer is attached to the peptidoglycan layerS-layer is attached to the outer membrane
12Teichoic acid present in the cell wallTeichoic acid absent in the cell wall
13Periplasmic space absent or if present, very narrowPeriplasmic space present
14Outer membrane absentOuter membrane present
15Lipid content very low (1-4%)Lipid content very high (11-22%)
16Porins (proteinaceous membrane channels) are absentPorins are present
17Lipopolysaccharides usually absentLipopolysaccharides present
18Mesosomes are more prominentMesosomes are less prominent
19Produce endospores spores during unfavourable conditionsUsually do not produce endospores
20Flagella with 2 rings in the basal bodyFlagella with four rings in the basal body
21Usually produce exotoxinsUsually produce endotoxins
22Gram positive bacteria are more susceptible to antibioticsGram negative bacteria are more resistant to antibiotics
23Can be killed by vancomycin antibioticCannot be killed by vancomycin antibiotic
24Shows high resistance to sodium azide solutionShows low resistance to sodium azide solution
25Cells shows high susceptibility towards penicillins and sulfonamide antibioticsCells shows low susceptibility towards penicillins and sulfonamide antibiotics
26Cells show low susceptibility towards streptomycin, chloramphenicol and tetracyclinesCells shows high susceptibility towards streptomycin, chloramphenicol and tetracyclines
27Cell wall is highly susceptible to degradation by lysozyme enzymeCell wall is less susceptible to degradation by lysozyme enzyme
28Shows high tolerance towards drynessShows low tolerance towards dryness
29Magnetosomes usually absentMagnetosomes sometimes present
30Very few are pathogenic to human and other animalsMost of them are pathogenic to human and other animals


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