Bacteria are broadly classified as gram-positive and gram-negative bacteria based on the Gram stain.
But both types are Prokaryotic cells and similar in many aspects.
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 they accept 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 the Cell wall layer | Entirely made of one component, i.e., mucopeptide. | Of the three components, (layers 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 the cell wall | The proportion of peptidoglycan present in the gram-positive bacteria is > 80%. | The proportion of the gram-negative bacteria is 2-12%. |
| 8 | Cell wall Thickness | Cell wall ranges between 15 to 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 alkali and is insoluble in 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 in cell wall | Teichoic acid is present. | Teichoic acid is absent |
| 14 | Periplasmic space | They do not have a periplasmic space. | They have a periplasmic space, which 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%. | Lipid content is high between 11- 22%. |
| 17 | Porin channels | The proteinaceous membrane channels called porins are absent in the cell wall. | The proteinaceous membrane channels are present in the outer membrane. |
| 18 | Lipopolysaccharides | Absent from the layer of the plasma membrane. | 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, they transform into endospores. | Usually, they 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 produce exotoxins. | Most 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 | Resistance to Sodium Azide | 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 | High tolerance to dryness (mucopeptide layer prevents water loss). | Low tolerance to dryness. |
| 28 | Magnetosomes | Absent in these bacteria | Present in some of them. |
| 29 | Pathogenicity | Very few of them are pathogenic to humans and animals. | Most are pathogenic to humans and animals |
| 30 | Examples | Staphylococcus, Bacillus subtilis, Streptococcus, Lactobacillus, Clostridium. | Pseudomonas, Klebsiella, Salmonella, Escherichia |
Similarities between them
- They both possess capsules.
- Both have 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.
