25 Differences between Gram-positive and Gram-negative bacteria

Bacteria are broadly classified as gram-positive and gram-negative bacteria based on gram stain.

But both the groups are Prokaryotic cells similar in many aspects. Check the similarities at the end after the table.

Differences between gram-positive and gram-negative bacteria

The two bacteria can be identified in a microbiology laboratory using a gram stain.

After staining, the color of the bacteria will be different.

Gram-positive and gram-negative stain
Sl.NoFeaturesGram +ve BacteriaGram-ve Bacteria
1Gram StainThe gram-positive bacteria will stain blue or purple when observed under a microscope.The gram-negative bacteria will stain pink or red under a microscope.
2Gram Stain ReactionThe bacteria will retain the crystal violet dye.The gram-negative bacteria cannot retain crystal violet, so it accepts the safranin dye.
3Cell wall layerThe cell wall is a single-layerThe cell wall is triple-layered.
Differences between gram positive and gram negative bacteria
Sl.NoFeaturesGram +ve BacteriaGram -ve Bacteria
4Cell wall layer componentsEntirely made of one component, i.e., mucopeptide.Each layer has (from outside to inside)
1. Lipoprotein
2. Lipopolysaccharide
3. Mucopeptide.
5Cell wall ShapeThe gram-positive bacteria contain flat and even cell walls.The gram-negative bacteria
contain wavy and uneven cell walls.
6ElasticityThe cell wall is very rigid and has minimal elasticity.The cell wall is less rigid, so it has high elasticity.
7Peptidoglycan in cell wallThe proportion of
peptidoglycan present in the gram-positive bacteria is > 80%.
The proportion in the gram-negative bacteria is 2-12%. 
8Cell wall ThicknessCell wall ranges between 15-20nm in thickness. Some of the bacteria contain an 80nm thickness cell wall.Here, the S-layer is attached to the
outer membrane.
9Muramic Acid
The muramic acid content in the gram-positive bacteria is 16-20%.The muramic acid content in the gram-negative bacteria is 2-5%.
10Cell wall ResistanceThe cell wall is resistant to the alkali and is insoluble in even a 1% KOH solution.It is sensitive to alkali and is soluble in 1% KOH solution.
11Resistance to Physical
The gram-positive cell is highly resistant to physical disruptions due to the presence of a rich peptidoglycan layerGram-negative bacteria are less resistant to physical damage
12S-layer (Surface layer in the cell wall)In the cell wall, the S-layer is attached to the peptidoglycan layer.Here the S-layer is attached to the
outer membrane.
13Teichoic acidAs seen in the diagram, Teichoic acid is present in the cell wall.Teichoic acid is absent
Peptidoglycan in the cell wallThe gram-negative bacteria have a periplasmic space. This differentiates the outer membrane and the plasma
15Outer membraneIt is absent here as the peptidoglycan layer makes up the whole layerIt is present above the thin layer of peptidoglycan
16Lipid ContentThe lipid content is low and is in the range of 1-4%.The gram-positive bacteria do not have periplasmic space.
17Porin channelsThe proteinaceous membrane channels called porins are absent
in the cell wall.
The proteinaceous membrane channels are distributed in the outer membrane.
18LipopolysaccharidesLipopolysaccharides are absent in the layer of the plasma membrane.Lipopolysaccharides are present in the layer
of the outer membrane.
19MesosomesMesosomes are prominent in the gram-negative.Mesosomes are less
prominent in the gram-negative.
20EndosporesDuring unfavorable conditions, the
bacteria transform into endospores.
Usually do not transform into endospores
21Flagella componentsThe basal body of the flagella in gram-positive bacteria contains two rings.The basal body of the flagella in gram-negative bacteria contains four rings.
22ToxinsMost of them can produce exotoxins.Most of them produce endotoxins.
23Antibiotic resistanceThey are less resistant to antibioticsModerately resistant to antibiotics
24Antibiotic susceptibilityBut show low susceptibility to antibiotics like aminoglycosides,
chloramphenicol and tetracyclines.
They show low to moderate susceptibility to next-generation penicillins and cephalosporins like
25The lipid content is very high, in the 11-22% range.Highly resistant to sodium azide solutionLess resistant to the
sodium azide solution.
The cell wall is highly susceptible to degradation by lysozyme enzymes.The cell wall is less susceptible to the lysozyme enzyme.
27Dry climate toleranceGram-positives have
a high tolerance to
dryness as the mucopeptide layer prevents water loss from cells.
Have less tolerance to dryness.

28MagnetosomesAbsent in these bacteriaSome of them have
29PathogenicityVery few of them are pathogenic to
humans and animals.
Most of them are pathogenic to
humans and animals
30ExamplesStaphylococcus, Bacillus subtitles,
Streptococcus, Lactobacillus,
Leuconostoc, Clostridium-like species.
They show high sensitivity to penicillin and sulfonamide antibiotics.

Similarities between them

  1. They both possess capsules.
  2. Both have the covalently closed circular DNA as the genetic material.
  3. They both contain extra-chromosomal genetic material (plasmids).
  4. Both undergo binary fission as a mode of asexual reproduction.
  5. Both groups included the flagellated (motile) and non-flagellated (non-motile) forms.

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