Gram-negative

Examples of Gram-negative in the following topics:

• Gram-Negative Outer Membrane

  • The Gram-negative cell wall is composed of an outer membrane, a peptidoglygan layer, and a periplasm.
  • In the Gram-negative Bacteria the cell wall is composed of a single layer of peptidoglycan surrounded by a membranous structure called the outer membrane.
  • The gram-negative bacteria do not retain crystal violet but are able to retain a counterstain, commonly safranin, which is added after the crystal violet.
  • The safranin is responsible for the red or pink color seen with a gram-negative bacteria.
  • Together, the plasma membrane and the cell wall (outer membrane, peptidoglycan layer, and periplasm) constitute the gram-negative envelope.

• The Deltaproteobacteria

  • All species of this group are, like all Proteobacteria, Gram-negative.
  • Myxobacteria are included among the delta group of proteobacteria, a large taxon of Gram-negative forms.

• The Entner–Doudoroff Pathway

  • Pseudomonas, a genus of Gram-negative bacteria, and Azotobacter, a genus of Gram-negative bacteria use the Entner-Doudoroff pathway
  • This pathway is generally found in Pseudomonas, Rhizobium, Azotobacter, Agrobacterium, and a few other Gram-negative genera.
  • Very few Gram-positive bacteria have this pathway, with Enterococcus faecalis being a rare exception.
  • Most organisms that use the pathway are aerobes due to the low ATP yield per glucose such as Pseudomonas, a genus of Gram-negative bacteria, and Azotobacter, a genus of Gram-negative bacteria.

• Spectrum of Antimicrobial Activity

  • Narrow spectrum antibiotics act against a limited group of bacteria, either gram positive or gram negative, for example sodium fusidate only acts against staphylococcal bacteria.
  • Broad spectrum—antibiotics act against gram positive and gram negative bacteria, for example amoxicillin.
  • Gram staining (or Gram's method; is a method of differentiating bacterial species into two large groups (Gram-positive and Gram-negative).
  • A Gram positive results in a purple/blue color while a Gram negative results in a pink/red color.
  • This is a microscopic image of a Gram stain of mixed Gram-positive cocci (Staphylococcus aureus, purple) and Gram-negative bacilli (Escherichia coli, red).

• Selective and Differential Media

  • Eosin methylene blue (EMB) that contains methylene blue – toxic to Gram-positive bacteria, allowing only the growth of Gram negative bacteria.
  • Mannitol salt agar (MSA) which is selective for Gram-positive bacteria and differential for mannitol.
  • Xylose lysine desoxyscholate (XLD), which is selective for Gram-negative bacteria buffered charcoal yeast extract agar, which is selective for certain gram-negative bacteria, especially Legionella pneumophila.

• Bacterial Pneumonias

  • Other commonly isolated bacteria include: Haemophilus influenzae in 20%, Chlamydophila pneumoniae in 13%, and Mycoplasma pneumoniae in 3% of cases; Staphylococcus aureus; Moraxella catarrhalis; Legionella pneumophila and Gram-negative bacilli.
  • Gram Positive.
  • Gram Negative.
  • Gram-negative bacteria are seen less frequently: Haemophilus influenzae , Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, and Moraxella catarrhalis are the most common.
  • In reality, they are "atypical" because they do not gram stain as well as gram-negative and gram-positive organisms.

• Peptidoglycan Synthesis and Cell Division

  • The peptidoglycan layer is substantially thicker in Gram-positive bacteria (20 to 80 nanometers) than in Gram-negative bacteria (7 to 8 nanometers), with the attachment of the S-layer.
  • Peptidoglycan forms around 90% of the dry weight of Gram-positive bacteria but only 10% of Gram-negative strains.
  • For both Gram-positive and Gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan.
  • Gram-positive and Gram-negative bacteria are sensitive to different types of antiobiotics.
  • Simplified sc hematic of a cell wall in a Gram-positive bacteria

• Gram-Positive Cell Envelope

  • Gram-positive bacteria are stained dark blue or violet by Gram staining .
  • A Gram-positive results in a purple/blue color while a Gram-negative results in a pink/red color.
  • They lack the outer membrane envelope found in Gram-negative bacteria.
  • Teichoic acids give the Gram-positive cell wall an overall negative charge due to the presence of phosphodiester bonds between teichoic acid monomers.
  • One idea is that they provide a channel of regularly-oriented, negative charges for threading positively-charged substances through the complicated peptidoglycan network.

• Phenotypic Analysis

  • Within prokaryotes, archaeal cell structure is most similar to that of Gram-positive bacteria.
  • The Gram stain, developed in 1884 by Hans Christian Gram, characterizes bacteria based on the structural characteristics of their cell walls.
  • The thick layers of peptidoglycan in the "Gram-positive" cell wall stain purple , while the thin "Gram-negative" cell wall appears pink.
  • By combining morphology and Gram-staining, most bacteria can be classified as belonging to one of four groups (Gram-positive cocci, Gram-positive bacilli, Gram-negative cocci, and Gram-negative bacilli).
  • Some organisms are best identified by stains other than the Gram stain, particularly mycobacteria or Nocardia, which show acid-fastness on Ziehl–Neelsen or similar stains.

• Actinobacteria (High G + C Gram-Positive Bacteria)

  • Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content in their DNA.
  • Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content in their DNA.
  • Unlike the Firmicutes, the other main group of Gram-positive bacteria, they have DNA with a high GC-content, and some Actinomycetes species produce external spores.
  • Classification of Gardnerella is controversial, and MeSH catalogues it as both a gram-positive and gram-negative organism.