Gram-negative bacteria are bacteria that, unlike gram-positive bacteria , do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is their cell envelope , which consists of a thin peptidoglycan cell wall sandwiched between an inner ( cytoplasmic ) membrane and an outer membrane . These bacteria are found in all environments that support life on Earth .
26-520: Verrucomicrobiota is a phylum of Gram-negative bacteria that contains only a few described species. The species identified have been isolated from fresh water , marine and soil environments and human faeces . A number of as-yet uncultivated species have been identified in association with eukaryotic hosts including extrusive explosive ectosymbionts of protists and endosymbionts of nematodes from genus Xiphinema , residing in their gametes . The verrucomicrobial bacterium Akkermansia muciniphila
52-459: A monophyletic clade and that no loss of the outer membrane from any species from this group has occurred. The proteobacteria are a major superphylum of gram-negative bacteria, including E. coli , Salmonella , Shigella , and other Enterobacteriaceae , Pseudomonas , Moraxella , Helicobacter , Stenotrophomonas , Bdellovibrio , acetic acid bacteria , Legionella etc. Other notable groups of gram-negative bacteria include
78-427: 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". Bacteria are traditionally classified based on their Gram-staining response into the gram-positive and gram-negative bacteria. Having just one membrane,
104-657: A few conserved signature indel (CSI) in the 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. They lack the GroEL signature. 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
130-652: A multitude of species. Some of them cause primarily respiratory problems ( Klebsiella pneumoniae , Legionella pneumophila , Pseudomonas aeruginosa ), primarily urinary problems ( Escherichia coli , Proteus mirabilis , Enterobacter cloacae , Serratia marcescens ), and primarily gastrointestinal problems ( Helicobacter pylori , Salmonella enteritidis , Salmonella typhi ). Gram-negative bacteria associated with hospital-acquired infections include Acinetobacter baumannii , which cause bacteremia , secondary meningitis , and ventilator-associated pneumonia in hospital intensive-care units . Transformation
156-435: A number of different observations, including that the gram-positive bacteria are the most sensitive to 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 . Some bacteria such as Deinococcus , which stain gram-positive due to
182-787: A toxic reaction when the bacteria are lysed by immune cells. This reaction may lead to septic shock , resulting in low blood pressure , respiratory failure , reduced oxygen delivery , and lactic acidosis . 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 . Conventional gram-negative (LPS-diderm) bacteria display
208-519: 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 . The outer membrane protects the bacteria from several antibiotics , dyes , and detergents that would normally damage either the inner membrane or the cell wall (made of peptidoglycan ). The outer membrane provides these bacteria with resistance to lysozyme and penicillin . The periplasmic space (space between
234-461: Is a human intestinal symbiotic bacterium that is considered as a promising probiotic. Verrucomicrobiota are abundant within the environment, though relatively inactive. This phylum is considered to have two sister phyla: Chlamydiota (formerly Chlamydiae) and Lentisphaerota (formerly Lentisphaerae) within the PVC superphylum . The Verrucomicrobiota phylum can be distinguished from neighbouring phyla within
260-530: Is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI) Gram-negative bacteria Within this category, notable species include the model organism Escherichia coli , along with various pathogenic bacteria , such as Pseudomonas aeruginosa , Chlamydia trachomatis , and Yersinia pestis . They pose significant challenges in
286-403: 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). In transformation, the genetic material passes through
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#1732851196111312-1323: Is the closest relative to Verrucomicrobiota , and that they are more closely related to one another than to the Planctomycetales . Verrucomicrobiota might belong in the clade Planctobacteria in the larger clade Gracilicutes . In 2008, the whole genome of Methylacidiphilum infernorum (2.3 Mbp ) was published. On the single circular chromosome , 2473 predicted proteins were found, 731 of which had no detectable homologs. These analyses also revealed many possible homologies with Pseudomonadota . Lentisphaeria Kiritimatiellae Opitutaceae Alterococcus Puniceicoccaceae "Pedosphaerales" Terrimicrobiaceae Verrucomicrobiaceae Akkermansiaceae Rubritaleaceae Lentisphaeraceae Oligosphaeraceae Victivallaceae "Spyradenecaceae" Kiritimatiellaceae Tichowtungiaceae Pontiellaceae Opitutaceae "Moanibacteraceae" Verruco-01 "Merdousiaceae" "Spyradosomataceae" "Cerasicoccaceae" "Coraliomargaritaceae" Puniceicoccaceae "Limisphaeraceae" "Pedosphaeraceae" "Methylacidiphilaceae" "Chthoniobacteraceae" "Udaeobacteraceae" Terrimicrobiaceae "Xiphinematobacteraceae" Akkermansiaceae SLCJ01 Verrucomicrobiaceae The currently accepted taxonomy
338-516: The CDC ), if any, governs the document being written. This is further explained at Gram staining § Orthographic note . List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature ( LPSN ) is an online database that maintains information on the naming and taxonomy of prokaryotes , following the taxonomy requirements and rulings of
364-616: The International Code of Nomenclature of Prokaryotes . The database was curated from 1997 to June 2013 by Jean P. Euzéby. From July 2013 to January 2020, LPSN was curated by Aidan C. Parte. In February 2020, a new version of LPSN was published as a service of the Leibniz Institute DSMZ , thereby also integrating the Prokaryotic Nomenclature Up-to-date service and since 2022 LPSN is interconnected with
390-474: The cyanobacteria , spirochaetes , green sulfur , and green non-sulfur bacteria . Medically-relevant gram-negative diplococci include the four types that cause a sexually transmitted disease ( Neisseria gonorrhoeae ), a meningitis ( Neisseria meningitidis ), and respiratory symptoms ( Moraxella catarrhalis , A coccobacillus Haemophilus influenzae is another medically relevant coccal type. Medically relevant gram-negative bacilli include
416-512: The PVC group by the presence of several conserved signature indels (CSIs). These CSIs represent unique, synapomorphic characteristics that suggest common ancestry within Verrucomicrobiota and an independent lineage amidst other bacteria. CSIs have also been found that are shared by Verrucomicrobiota and Chlamydiota exclusively of all other bacteria. These CSIs provide evidence that Chlamydiota
442-420: The diderm bacteria in which the outer cell membrane is made up of mycolic acid (e. g. Mycobacterium ). The conventional LPS- diderm group of gram-negative bacteria (e.g., Pseudomonadota , Aquificota , Chlamydiota , Bacteroidota , Chlorobiota , " Cyanobacteria ", Fibrobacterota , Verrucomicrobiota , Planctomycetota , Spirochaetota , Acidobacteriota ; " Hydrobacteria ") are uniquely identified by
468-518: The following characteristics : 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.). Since 1987, the monophyly of the gram-negative bacteria has been disproven with molecular studies . However some authors, such as Cavalier-Smith still treat them as
494-487: The gram-positive bacteria are also known as 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
520-830: The intervening medium, and uptake is completely dependent on the recipient bacterium. 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. 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 . 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 . One of
546-440: The medical field due to their outer membrane, which acts as a protective barrier against numerous antibiotics (including penicillin ), detergents that would normally damage the inner cell membrane, and the antimicrobial enzyme lysozyme produced by animals as part of their innate immune system . Furthermore, the outer leaflet of this membrane contains a complex lipopolysaccharide (LPS) whose lipid A component can trigger
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#1732851196111572-509: 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 . The adjectives gram-positive and gram-negative derive from the surname of Hans Christian Gram , a Danish bacteriologist; as eponymous adjectives , their initial letter can be either capital G or lower-case g , depending on which style guide (e.g., that of
598-419: 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. 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
624-459: The several unique characteristics of gram-negative bacteria is the structure of the bacterial outer membrane . The outer leaflet of this membrane contains lipopolysaccharide (LPS), whose lipid A portion acts as an endotoxin . If gram-negative bacteria enter the circulatory system , LPS can trigger an innate immune response , activating the immune system and producing cytokines (hormonal regulators). This leads to inflammation and can cause
650-426: The staining result. 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 . Of these two structurally distinct groups of prokaryotic organisms, monoderm prokaryotes are thought to be ancestral. Based upon
676-403: The two cell membranes) also contains enzymes which break down or modify antibiotics. Drugs commonly used to treat gram negative infections include amino, carboxy and ureido penicillins ( ampicillin , amoxicillin , pipercillin , ticarcillin ). These drugs may be combined with beta-lactamase inhibitors to combat the presence of enzymes that can digest these drugs (known as beta-lactamases ) in
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