Gram-negative bacteria
(Redirected from
Gram negative
)
Gram-negative bacteria are
cell wall sandwiched between an inner (cytoplasmic) membrane and an outer membrane.[citation needed] These bacteria are found in all environments that support life on Earth
.
Within this category, notable species include the
reduced oxygen delivery, and lactic acidosis.[2]
Several
classes of antibiotics have been developed to target gram-negative bacteria, including aminopenicillins, ureidopenicillins, cephalosporins, beta-lactam-betalactamase inhibitor combinations (such as piperacillin-tazobactam), folate antagonists, quinolones, and carbapenems. Many of these antibiotics also cover gram-positive bacteria. The antibiotics that specifically target gram-negative organisms include aminoglycosides, monobactams (such as aztreonam), and ciprofloxacin
.
Characteristics
Conventional gram-negative (LPS-diderm) bacteria display the following characteristics:[citation needed]
- An inner cell membrane is present (cytoplasmic)
- A thin peptidoglycan layer is present (this is much thicker in gram-positive bacteria)
- Has O antigen) in its outer leaflet and phospholipidsin the inner leaflet
- Porins exist in the outer membrane, which act like pores for particular molecules
- Between the outer membrane and the cytoplasmic membrane there is a space filled with a concentrated gel-like substance called periplasm
- The S-layer is directly attached to the outer membrane rather than to the peptidoglycan
- If present, flagellahave four supporting rings instead of two
- Teichoic acids or lipoteichoic acids are absent
- Lipoproteins are attached to the polysaccharide backbone
- Some contain Braun's lipoprotein, which serves as a link between the outer membrane and the peptidoglycan chain by a covalent bond
- Most, with few exceptions, do not form spores
Classification
Along with cell shape, Gram staining is a rapid diagnostic tool and once was used to group species at the subdivision of Bacteria. Historically, the kingdom Monera was divided into four divisions based on Gram staining: Firmacutes (+), Gracillicutes (−), Mollicutes (0) and Mendocutes (var.).[3] Since 1987, the
Cavalier-Smith still treat them as a monophyletic taxon (though not a clade; his definition of monophyly requires a single common ancestor but does not require holophyly, the property that all descendants be encompassed by the taxon) and refer to the group as a subkingdom "Negibacteria".[5]
Taxonomy
 | This section may be too technical for most readers to understand. (March 2014) |
 | It has been suggested that this section be split out into another article titled Gram stain. (Discuss) (November 2023) |
Bacteria are traditionally classified based on their
monoderm bacteria, while gram-negative bacteria, having two membranes, are also known as diderm bacteria. It was traditionally thought that the groups represent lineages, i.e., the extra membrane only evolved once, such that gram-negative bacteria are more closely related to one another than to any gram-positive bacteria. While this is often true, the classification system breaks down in some cases, with lineage groupings not matching the staining result.[6][7][8][9] Thus, Gram staining cannot be reliably used to assess familial relationships of bacteria. Nevertheless, staining often gives reliable information about the composition of the cell membrane, distinguishing between the presence or absence of an outer lipid membrane.[6][10]
Of these two structurally distinct groups of
antibiotics and that the gram-negative bacteria are, in general, resistant to antibiotics, it has been proposed that the outer cell membrane in gram-negative bacteria (diderms) evolved as a protective mechanism against antibiotic selection pressure.[6][7][10][11] Some bacteria such as Deinococcus, which stain gram-positive due to the presence of a thick peptidoglycan layer, but also possess an outer cell membrane are suggested as intermediates in the transition between monoderm (gram-positive) and diderm (gram-negative) bacteria.[6][11] The diderm bacteria can also be further differentiated between simple diderms lacking lipopolysaccharide (LPS); the archetypical diderm bacteria, in which the outer cell membrane contains lipopolysaccharide; and the diderm bacteria, in which the outer cell membrane is made up of mycolic acid (e. g. Mycobacterium).[8][9][11][12]
The conventional LPS-diderm group of gram-negative bacteria (e.g.,
HSP60 (GroEL) protein. In addition, a number of bacterial taxa (including Negativicutes, Fusobacteriota, Synergistota, and Elusimicrobiota) that are either part of the phylum Bacillota (a monoderm group) or branches in its proximity are also found to possess a diderm cell structure.[9][11][12] They lack the GroEL signature.[11] The presence of this CSI in all sequenced species of conventional lipopolysaccharide-containing gram-negative bacterial phyla provides evidence that these phyla of bacteria form a monophyletic clade and that no loss of the outer membrane from any species from this group has occurred.[11]
Example species
The
green non-sulfur bacteria[13].[citation needed
]
Medically-relevant gram-negative
sexually transmitted disease (Neisseria gonorrhoeae[14]), a meningitis (Neisseria meningitidis[15]), and respiratory symptoms (Moraxella catarrhalis,[16] A coccobacillus Haemophilus influenzae is another medically relevant coccal type.[17]
Medically relevant gram-negative
Salmonella typhi).[citation needed
]
Gram-negative bacteria associated with
intensive-care units
.
Bacterial transformation
Transformation is one of three processes for horizontal gene transfer, in which exogenous genetic material passes from one bacterium to another, the other two being conjugation (transfer of genetic material between two bacterial cells in direct contact) and transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium).[18][19] In transformation, the genetic material passes through the intervening medium, and uptake is completely dependent on the recipient bacterium.[18]
As of 2014 about 80 species of bacteria were known to be capable of transformation, about evenly divided between
gram-positive and gram-negative bacteria; the number might be an overestimate since several of the reports are supported by single papers.[18] Transformation has been studied in medically important gram-negative bacteria species such as Helicobacter pylori, Legionella pneumophila, Neisseria meningitidis, Neisseria gonorrhoeae, Haemophilus influenzae and Vibrio cholerae.[20] It has also been studied in gram-negative species found in soil such as Pseudomonas stutzeri, Acinetobacter baylyi, and gram-negative plant pathogens such as Ralstonia solanacearum and Xylella fastidiosa.[20]
Role in disease
MALDI-TOF
and/or multitarget assay.One of the several unique characteristics of gram-negative bacteria is the structure of the
innate immune response, activating the immune system and producing cytokines (hormonal regulators). This leads to inflammation and can cause a toxic reaction, resulting in fever, an increased respiratory rate, and low blood pressure. That is why some infections with gram-negative bacteria can lead to life-threatening septic shock.[2]
The outer membrane protects the bacteria from several
beta-lactamase inhibitors to combat the presence of enzymes that can digest these drugs (known as beta-lactamases) in the peri-plasmic space. Other classes of drugs that have gram negative spectrum include cephalosporins, monobactams (aztreonam), aminoglycosides, quinolones, macrolides, chloramphenicol, folate antagonists, and carbapenems.[21]
Orthographic note
The adjectives gram-positive and gram-negative derive from the surname of
Gram staining § Orthographic note
.
See also
References
This article incorporates NCBI. Archived from the originalon 2009-12-08.
Notes
- ^ from the original on 2021-07-06. Retrieved 2021-08-18.
- ^ from the original on 2022-04-13. Retrieved 2021-05-12.
- .
- PMID 2439888.
- PMID 16834776.
- ^ PMID 9841678.
- ^ (PDF) from the original on 2018-07-20. Retrieved 2017-10-24.
- ^ PMID 19299134.
- ^ PMID 20637628.
- ^ PMID 9723910.
- ^ PMID 21717204.
- ^ PMID 19667386.
- PMID 21413290, retrieved 2024-03-28
- PMID 30026943.
- ^ "Vaccine Preventable Diseases Surveillance Manual". CDC. April 3, 2018. Retrieved January 26, 2024.
- PMID 11781271.
- ^ "For Clinicians: Haemophilus influenzae". CDC. February 13, 2018. Retrieved January 26, 2024.
- ^ S2CID 23559881.
- PMID 36838287.
- ^ PMID 22928673.
- ^ Glück, Thomas (12 December 2003). "Gram-Negative Bacteria and Broad-Spectrum Antibiotics: Good News Except for Fluoroquinolones". www.jwatch.org. NEJM Journal Watch. Archived from the original on 10 March 2018. Retrieved 10 March 2018.
- ^ "Preferred Usage - Emerging Infectious Disease journal - CDC". CDC.gov. Centers for Disease Control and Prevention. Archived from the original on 2018-01-29. Retrieved 2018-03-04.
External links
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