Gram Positive and Negative Bacteria – Class 11 | Chapter – 2 | Short Notes Series PDF
Gram Positive and Negative Bacteria: Gram-positive bacteria are bacteria with thick cell walls. In a Gram stain test, these organisms yield a positive result. The test, which involves a chemical dye, stains the bacterium’s cell wall purple.
Gram-negative bacteria, on the other hand, don’t hold the dye. They stain pink instead.
Though both groups of bacteria can cause disease, they require different treatments. If you have a bacterial infection, the Gram stain will determine what kind of medication you need.
Gram-negative bacteria can cause many serious infections, such as pneumonia, peritonitis (inflammation of the membrane that lines the abdominal cavity), urinary tract infections, bloodstream infections, wound or surgical site infections, and meningitis.
Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining is used on them. Gram-negative bacteria stain red when this process is used.
Gram-positive bacteria stain blue.
Gram-negative and gram-positive bacteria stain differently because their cell walls are different. They also cause different types of infections, and different types of antibiotics are effective against them.
Difference between Gram Positive and Negative Bacteria
| Basis of Difference | Gram-Positive bacteria | Gram-Negative bacteria |
| Cell Wall | A single-layered, smooth cell wall | A double-layered, wavy cell-wall |
| Cell Wall thickness | The thickness of the cell wall is 20 to 80 nanometres | The thickness of the cell wall is 8 to 10 nanometres |
| Peptidoglycan Layer | It is a thick layer/ also can be multilayered | It is a thin layer/ often single-layered. |
| Teichoic acids | Presence of teichoic acids | Absence of teichoic acids |
| Outer membrane | The outer membrane is absent | The outer membrane is present (mostly) |
| Porins | Absent | Occurs in Outer Membrane |
| Mesosome | It is more prominent. | It is less prominent. |
| Morphology | Cocci or spore-forming rods | Non-spore forming rods. |
| Flagella Structure | Two rings in basal body | Four rings in basal body |
| Lipid content | Very low | 20 to 30% |
| Lipopolysaccharide | Absent | Present |
| Toxin Produced | Exotoxins | Endotoxins or Exotoxins |
| Resistance to Antibiotic | More susceptible | More resistant |
| Examples | Staphylococcus, Streptococcus, etc. | Escherichia, Salmonella, etc. |
| Gram Staining | These bacteria retain the crystal violet colour even after they are washed with acetone or alcohol and appear as purple-coloured when examined under the microscope after gram staining. | These bacteria do not retain the stain colour even after they are washed with acetone or alcohol and appear as pink-coloured when examined under the microscope after gram staining. |
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