Gram-Negative Bacteria

A Gram-Negative Bacteria is a bacteria that fails to retain crystal violet dye during Gram staining protocols due to its distinct cell wall structure.

• AKA: Gram-negative Microorganism, Gram-negative Bacterium.
• Context:
  • It can typically possess a thin peptidoglycan layer between its inner cytoplasmic membrane and outer membrane.
  • It can typically contain lipopolysaccharide (LPS) in its outer membrane, which functions as an endotoxin during infection.
  • It can typically appear pink or red after Gram staining procedures due to the counterstain (usually safranin).
  • It can typically display increased antibiotic resistance compared to gram-positive bacteria due to its protective outer membrane.
  • It can typically cause immune system activation through lipopolysaccharide recognition by host receptors.
  • ...
  • It can often trigger inflammatory responses in host organisms through cytokine production pathways.
  • It can often produce pathogenic effects in human and animal hosts through specific virulence factors.
  • It can often contain porins in the outer membrane that regulate molecular transport across the bacterial envelope.
  • It can often harbor beta-lactamase enzymes that provide resistance to many beta-lactam antibiotics.
  • ...
  • It can range from being a Non-Pathogenic Gram-Negative Bacteria to being a Highly Pathogenic Gram-Negative Bacteria, depending on its virulence factor expression.
  • It can range from being a Simple Gram-Negative Bacteria to being a Complex Gram-Negative Bacteria, depending on its metabolic capability and genetic composition.
  • It can range from being an Aerobic Gram-Negative Bacteria to being an Anaerobic Gram-Negative Bacteria, depending on its oxygen requirement.
  • ...
  • It can be classified into various phylogenetic groups based on genetic sequences, biochemical propertys, and morphological characteristics.
  • It can be identified through laboratory techniques including Gram staining, biochemical tests, and molecular analysis.
  • It can cause diverse infections affecting different body systems including respiratory tract, urinary tract, gastrointestinal system, and bloodstream.
  • ...
• Examples:
  • Gram-Negative Bacteria Familys, such as:
    • Enterobacteriaceae containing important pathogens like Escherichia coli, Salmonella, Shigella, and Klebsiella.
    • Pseudomonadaceae including Pseudomonas aeruginosa associated with hospital-acquired infections.
    • Vibrionaceae featuring Vibrio cholerae, the causative agent of cholera.
  • Gram-Negative Bacteria Morphologys, such as:
    • Rod-shaped Gram-Negative Bacteria (bacilli) including Escherichia coli and Salmonella species.
    • Curved Gram-Negative Bacteria such as Vibrio and Campylobacter species.
    • Spherical Gram-Negative Bacteria (cocci) including Neisseria species.
  • Gram-Negative Bacteria Clinical Significances, such as:
    • Respiratory Gram-Negative Bacteria including Haemophilus influenzae and Legionella pneumophila.
    • Enteric Gram-Negative Bacteria causing gastrointestinal diseases like Salmonella, Shigella, and Escherichia coli.
    • Sexually Transmitted Gram-Negative Bacteria such as Neisseria gonorrhoeae.
  • Gram-Negative Bacteria Environmental Habitats, such as:
    • Soil-Dwelling Gram-Negative Bacteria including various Pseudomonas species.
    • Aquatic Gram-Negative Bacteria such as Vibrio species and Legionella.
    • Host-Associated Gram-Negative Bacteria found in normal microbiota of human and animal bodies.
  • ...
• Counter-Examples:
  • Gram-Positive Bacteria, which retain crystal violet dye during Gram staining due to their thick peptidoglycan layer and lack of outer membrane.
  • Acid-Fast Bacteria, which have unique cell wall composition with mycolic acids requiring specialized staining techniques.
  • Mycoplasma, which lack cell wall structures entirely and thus cannot be classified by Gram staining methods.
• See: Bacteria, Bacterial Cell Wall, Gram Staining, Lipopolysaccharide, Endotoxin, Bacterial Pathogenesis, Antibiotic Resistance, Microbiology, Crystal Violet, Safranin.

---

---

References

2009

• (Wikipedia, 2009) ⇒ http://en.wikipedia.org/wiki/Gram-negative
  • Gram-negative bacteria are those bacteria that do not retain crystal violet dye in the Gram staining protocol. [1] In a Gram stain test, a counterstain (commonly safranin) is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color. The test itself is useful in classifying two distinct types of bacteria based on the structural differences of their cell walls. On the other hand, Gram-positive bacteria will retain the crystal violet dye when washed in a decolorizing solution.

    Many species of Gram-negative bacteria are pathogenic, meaning that they can cause disease in a host organism. This pathogenic capability is usually associated with certain components of Gram-negative cell walls, in particular the lipopolysaccharide (also known as LPS or endotoxin) layer. [1] In humans, LPS triggers an innate immune response characterized by cytokine production and immune system activation. Inflammation is a common result of cytokine(from the greek cyto=cell,kinesis=movement) production, which can also produce host toxicity.

---