Question

Describe the medical relevance of the Gram positive cell walls and the Gram negative cell walls

Answer 1

Answer:

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Gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their cell wall.

Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test.

Gram-negative bacteria cannot retain the violet stain after the decolorization step; alcohol used in this stage degrades the outer membrane of gram-negative cells, making the cell wall more porous and incapable of retaining the crystal violet stain. Their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain (safranin or fuchsine) and appear red or pink.

Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to certain cell wall targeting antibiotics than Gram-negative bacteria, due to the absence of the outer membrane.[1]

Answer 2

Gram-Positive bacteria Gram-Negative bacteria
Cell Wall
Their cell wall is smooth and single-layered They have a wavy and double-layered 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 It is a thin layer
Teichoic acids
Presence of teichoic acids Absence of teichoic acids
Outer membrane
The outer membrane is absent The outer membrane is present
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
2 rings in basal body 4 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.