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