Gram-Negative Bacteria

Gram-Negative Bacteria

Gram-negative bacteria are the genus of bacteria family and a member of the phylum Firmicutes. They are the group of aerobic bacterium which does not retain the crystal violet dye during the procedure of Gram staining and they appear pink in color when they are examined under the microscope.

There are many gram-negative bacteria of medical significance. The most important of these are members of the family Enterobacteriaceae. Further genera of Gram-negative bacteria include Vibrio, Campylobacter, Pseudomonas, and other bacteria which are normally found in the gastrointestinal tract.

General Characteristics of Gram-Negative Bacteria

  • Free-living
  • Rod-shaped, the non-motile bacterium.
  • Reduce nitrates into nitrites.
  • Ferment glucose with acid production.
  • They are good decomposers and bioremediations.
  • Abundantly found in soil, sea water, fresh water, in colonizing plants and animals, and in the intestines of humans and animals.

Cell Structures of Gram-Negative Bacteria

Gram-Negative Bacteria cell wall

  • The cell wall of Gram-negative bacteria is thin and is composed of peptidoglycan.
  • The cell envelope has 3 layers including, a unique outer membrane, a thin peptidoglycan layer, and the cytoplasmic membrane.
  • An outer membrane of the cell wall is a bilayer structure consisting of phospholipids molecules, lipopolysaccharides (LPS), lipoproteins and surface proteins.
  • Endotoxin is toxins released by the cell during infections and function as receptors and blocking immune response.
  • The porin proteins are present in the upper layer of a cell which functions by regulating the entry and exit of the molecules within the cell.

Pathogenesis in Humans

The diseases caused by gram-negative bacteria are diarrhea, inflammatory disease of the large intestine, infantile diarrhea, kidney damage, typhoid fever, bubonic plague, cholera etc.

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