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.

Sl.No	Features	Gram +ve Bacteria	Gram-ve Bacteria
1	Gram Stain	The 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.
2	Reaction to Gram Stain	The bacteria will retain the crystal violet dye.	The gram-negative bacteria cannot retain crystal violet, so it accepts the safranin dye.
3	Cell wall layer	The cell wall is a single-layer	The cell wall is triple-layered.

Sl.No	Features	Gram +ve Bacteria	Gram -ve Bacteria
4	Components of Cell wall layer	Entirely made of one component, i.e., mucopeptide.	Each layer has (from outside to inside) 1. Lipoprotein 2. Lipopolysaccharide 3. Mucopeptide.
5	Cell wall Shape	The gram-positive bacteria contain flat and even cell walls.	The gram-negative bacteria contain wavy and uneven cell walls.
6	Elasticity	The cell wall is very rigid and has minimal elasticity.	The cell wall is less rigid, so it has high elasticity.
7	Peptidoglycan in cell wall	The proportion of peptidoglycan present in the gram-positive bacteria is > 80%.	The proportion in the gram-negative bacteria is 2-12%.
8	Cell wall Thickness	Cell 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.
9	Muramic Acid Content	The muramic acid content in the gram-positive bacteria is 16-20%.	The muramic acid content in the gram-negative bacteria is 2-5%.
10	Cell wall Resistance	The 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.
11	Resistance to Physical Disruptions	The gram-positive cell is highly resistant to physical disruptions due to the presence of a rich peptidoglycan layer	Gram-negative bacteria are less resistant to physical damage
12	S-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.
13	Teichoic acid	As seen in the diagram, Teichoic acid is present in the cell wall.	Teichoic acid is absent
14	Periplasmic space	Peptidoglycan in the cell wall	The gram-negative bacteria have a periplasmic space. This differentiates the outer membrane and the plasma membrane.
15	Outer membrane	It is absent here as the peptidoglycan layer makes up the whole layer	It is present above the thin layer of peptidoglycan
16	Lipid Content	The lipid content is low and is in the range of 1-4%.	The gram-positive bacteria do not have periplasmic space.
17	Porin channels	The proteinaceous membrane channels called porins are absent in the cell wall.	The proteinaceous membrane channels are distributed in the outer membrane.
18	Lipopolysaccharides	Lipopolysaccharides are absent in the layer of the plasma membrane.	Lipopolysaccharides are present in the layer of the outer membrane.
19	Mesosomes	Mesosomes are prominent in the gram-negative.	Mesosomes are less prominent in the gram-negative.
20	Endospores	During unfavorable conditions, the bacteria transform into endospores.	Usually do not transform into endospores
21	Flagella components	The 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.
22	Toxins	Most of them can produce exotoxins.	Most of them produce endotoxins.
23	Antibiotic resistance	They are less resistant to antibiotics	Moderately resistant to antibiotics
24	Antibiotic susceptibility	But show low susceptibility to antibiotics like aminoglycosides, chloramphenicol and tetracyclines.	They show low to moderate susceptibility to next-generation penicillins and cephalosporins like antibiotics.
25	The lipid content is very high, in the 11-22% range.	Highly resistant to sodium azide solution	Less resistant to the sodium azide solution.
26	Lysozyme susceptibility	The cell wall is highly susceptible to degradation by lysozyme enzymes.	The cell wall is less susceptible to the lysozyme enzyme.
27	Dry climate tolerance	Gram-positives have a high tolerance to dryness as the mucopeptide layer prevents water loss from cells.	Have less tolerance to dryness.
28	Magnetosomes	Absent in these bacteria	Some of them have
29	Pathogenicity	Very few of them are pathogenic to humans and animals.	Most of them are pathogenic to humans and animals
30	Examples	Staphylococcus, 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.