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Gram-negative bacteria are
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
that do not retain the
crystal violet Crystal violet or gentian violet, also known as methyl violet 10B or hexamethyl pararosaniline chloride, is a triphenylmethane, triarylmethane dye used as a histological stain and in Gram staining, Gram's method of classifying bacteria. Crystal v ...
stain used in the
Gram stain Gram stain or Gram staining, also called Gram's method, is a method of staining specimen, sandwiched between a glass microscope slide. Staining is a technique used to enhance contrast in samples, generally at the Microscope, microscopic leve ...

Gram stain
ing method of bacterial differentiation. They are characterized by their
cell envelopeThe cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In gram-negative bacteria an bacterial outer membrane, outer membrane is also included. This envelope is not present in the Mollicutes where the cell wall is absen ...
s, which are composed of a thin
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repea ...

peptidoglycan
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
sandwiched between an inner
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
ic
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membra ...

cell membrane
and a
bacterial outer membrane 350px, Structure of gram-negative cell envelope The bacterial outer membrane is found in gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bact ...
. Gram-negative bacteria are found in virtually all environments on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
that support life. The gram-negative bacteria include the
model organism A model organism (often shortened to model) is a non-human species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is ...
''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative bacteria, Gram-negative, Facultative anaerobic organism, facultative anaer ...

Escherichia coli
'', as well as many
pathogenic bacteria Pathogenic bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, such as ''
Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation. They are characterized ...
'', ''
Chlamydia trachomatis ''Chlamydia trachomatis'' (), commonly known as chlamydia, is a bacterium that causes chlamydia Chlamydia, or more specifically a chlamydia infection, is a sexually transmitted infection caused by the bacterium '' Chlamydia trachomatis''. Mo ...
'', and ''
Yersinia pestis ''Yersinia pestis'' (''Y. pestis'') (formerly ''Pasteurella __NOTOC__ ''Pasteurella'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the ...

Yersinia pestis
''. They are an important medical challenge, as their outer membrane protects them from many
antibiotic An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system t ...
s (including
penicillin Penicillins (P, PCN or PEN) are a group of originally obtained from ' s, principally ' and '. Most penicillins in clinical use are chemically synthesised from naturally-produced penicillins. A number of natural penicillins have been discov ...

penicillin
),
detergent A detergent is a surfactant Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting ...
s that would normally damage the inner cell membrane, and
lysozyme Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, is an antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an ...

lysozyme
, an
antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All orga ...
enzyme produced by animals that forms part of the
innate immune system The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the d ...

innate immune system
. Additionally, the outer leaflet of this membrane comprises a complex
lipopolysaccharide Lipopolysaccharides (LPS), also known as endotoxins, are large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

lipopolysaccharide
(LPS) whose
lipid A Lipid A is a lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) dissolve in water, including s, es, s, fat-soluble s ...

lipid A
component can cause a toxic reaction when bacteria are lysed by immune cells. This toxic reaction lead to
low blood pressure Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dia ...
,
respiratory failure Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise i ...

respiratory failure
, reduced oxygen delivery, and
lactic acidosis Lactic acidosis is a medical condition characterized by the buildup of lactate (especially L-lactate Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)COOH. It is white in the solid state and it is miscibility, miscible with w ...
—a life-threatening condition known as
septic shock Septic shock (namely, '' infection throughout the body'') is a potentially fatal medical condition that occurs when sepsis, which is organ injury or damage in response to infection An infection is the invasion of an organism's body Tissue (b ...
. Several
classes of antibiotic
classes of antibiotic
s have been designed to target gram-negative bacteria, including
aminopenicillin The aminopenicillins are a group of antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antib ...

aminopenicillin
s,
ureidopenicillin The ureidopenicillins are a group of penicillins which are active against ''Pseudomonas aeruginosa''. There are three ureidopenicillins in clinical use: *Azlocillin *Piperacillin *Mezlocillin They are mostly ampicillin derivatives in which the ...
s,
cephalosporin The cephalosporins (sg. ) are a class of β-lactam antibiotics originally derived from the fungus A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeast ...
s,
beta-lactam A beta-lactam (β-lactam) ring is a four-membered lactam. A ''lactam'' is a cyclic amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula RC(=O)NR′R″, where R, R', ...

beta-lactam
- betalactamase inhibitor combinations (e.g. piperacillin-tazobactam), Folate antagonists,
quinolone
quinolone
s, and
carbapenem Carbapenems are a class of highly effective antibiotic An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, a ...

carbapenem
s. Many of these antibiotics also cover
gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
organisms. The drugs that specifically target gram negative organisms include
aminoglycoside Aminoglycoside is a medicinal chemistry, medicinal and bacteriology, bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside ( ...
s,
monobactam Monobactams are monocyclic and bacterially-produced β-lactam antibiotics. The β-lactam A beta-lactam (β-lactam) ring is a four-membered lactam A lactam is a cyclic amide. The term is a portmanteau of the words '' lactone'' + '' amide''. ...
s (
aztreonam
aztreonam
) and
ciprofloxacin Ciprofloxacin is an antibiotic used to treat a number of bacterial infections. This includes bone and joint infections, intra abdominal infections, certain type of infectious diarrhea, respiratory tract infections, skin infections, typhoid f ...

ciprofloxacin
.


Characteristics

Gram-negative bacteria display : *An inner
cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane A biological membrane, biomembrane or cell membrane is a selectively permeable membra ...

cell membrane
is present (
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
ic) * A thin
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repea ...

peptidoglycan
layer is present (this is much thicker in
gram-positive bacteria In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
) * Has outer membrane containing
lipopolysaccharide Lipopolysaccharides (LPS), also known as endotoxins, are large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

lipopolysaccharide
s (LPS, which consists of
lipid A Lipid A is a lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) dissolve in water, including s, es, s, fat-soluble s ...

lipid A
, core
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallograp ...
, and
O antigen Lipopolysaccharides (LPS), also known as endotoxins, are large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...
) in its outer leaflet and
phospholipid Phospholipids, also known as phosphatides, are a class of lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) disso ...

phospholipid
s in the inner leaflet * Porins exist in the outer membrane, which act like pores for particular molecules * Between the outer membrane and the
cytoplasmic membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates the interior of all cells from the out ...

cytoplasmic membrane
there is a space filled with a concentrated gel-like substance called
periplasm 400px, cell_wall.html"_;"title="Gram-negative_cell_wall">Gram-negative_cell_wall_ The_periplasm_is_a_concentrated_gel-like_matrix_(biology).html" ;"title="cell_wall_.html" ;"title="cell_wall.html" ;"title="Gram-negative cell wall">Gram-negative ce ...
* The
S-layer An S-layer (surface layer) is a part of the cell envelope found in almost all archaea, as well as in many types of bacteria. The S-layers of both archaea and bacteria consists of a monomolecular layer composed of only one (or, in a few cases, two) i ...
is directly attached to the outer membrane rather than to the
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repea ...

peptidoglycan
* If present,
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and ...

flagella
have four supporting rings instead of two *
Teichoic acid Teichoic acids (''cf.'' Greek τεῖχος, ''teīkhos'', "wall", to be specific a fortification wall, as opposed to τοῖχος, ''toīkhos'', a regular wall) are bacterial copolymers of glycerol phosphate or ribitol, ribitol phosphate and c ...
s or
lipoteichoic acid Lipoteichoic acid (LTA) is a major constituent of the cell wall of gram-positive 300px, Violet-stained gram-positive cocci and pink-stained gram-negative bacillus (shape), bacilli In bacteriology, gram-positive bacteria are bacteria that give ...

lipoteichoic acid
s are absent *
Lipoprotein 250px, Structure of a chylomicron. ApoA, ApoB, ApoC, ApoE are apolipoproteins; green particles are phospholipids; T is triacylglycerol; C is cholesterol ester. A lipoprotein is a biochemical assembly whose primary function is to transport hydropho ...
s 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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...


Classification

Along with cell shape,
Gram stain Gram stain or Gram staining, also called Gram's method, is a method of staining specimen, sandwiched between a glass microscope slide. Staining is a technique used to enhance contrast in samples, generally at the Microscope, microscopic leve ...

Gram stain
ing is a rapid diagnostic tool and once was used to group species at the subdivision of Bacteria.
Historically History (from Ancient Greek, Greek , ''historia'', meaning "inquiry; knowledge acquired by investigation") is the study of the past. Events occurring before the History of writing#Inventions of writing, invention of writing systems are considered ...

Historically
, the kingdom
Monera Monera (/məˈnɪərə/) (Greek - μονήρης (monḗrēs), "single", "solitary") is a biological kingdom that is made up of prokaryote A prokaryote () is a Unicellular organism, single-celled organism that lacks a cell nucleus, nucleus, a ...
was divided into four
divisions Division or divider may refer to: Mathematics *Division (mathematics) Division is one of the four basic operations of arithmetic, the ways that numbers are combined to make new numbers. The other operations are addition, subtraction, and multi ...
based on Gram staining:
Firmacutes The Firmicutes (Latin: ''firmus'', strong, and ''cutis'', skin, referring to the cell wall) are a phylum of bacteria, most of which have gram-positive bacteria, gram-positive cell wall structure. A few, however, such as ''Megasphaera'', ''Pectinatu ...
(+), Gracillicutes (−),
Mollicutes Mollicutes is a class of bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micromet ...
(0) and Mendocutes (var.). Since 1987, the
monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
of the gram-negative bacteria has been disproven with molecular studies. However some authors, such as
Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 - 19 March 2021), was a Professor of Evolutionary Biology Evolutionary biology is the subfield of biology that studies the evolution, evolutionary processes ...
still treat them as a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
(though not a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
; his definition of
monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
requires a single common ancestor but does not require holophyly, the property that all descendants be encompassed by the
taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
) and refer to the group as a
subkingdom In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...
"Negibacteria".


Taxonomy

Bacteria are traditionally classified based on their
Gram-stain
Gram-stain
ing response into the
gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacte ...
and gram-negative bacteria. Having just one membrane the gram-positive bacteria are also known as monoderm bacteria, and gram-negative 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. 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 A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual conti ...
organisms, monoderm prokaryotes are thought to be ancestral. Based upon a number of different observations including that the gram-positive bacteria are the most sensitive to
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy, ...
and that gram-negative bacteria are, in general, to them, it has been proposed that the outer cell membrane in gram-negative bacteria (diderms) evolved as a protective mechanism against antibiotic
selection pressure Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection Natural selection is the differential survi ...
. Some bacteria such as ''
Deinococcus ''Deinococcus'' (from the el, δεινός, ''deinos'', "dreadful, strange" and κόκκος, ''kókkos'', "granule") is one genus of three in the order Deinococcales of the bacterial phylum ''Deinococcus''-''Thermus'' highly resistant to envir ...
'', which stain gram-positive due to the presence of a thick
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repea ...

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 the diderm bacteria, in which the outer cell membrane is made up of
mycolic acidMycolic acids are long fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistry is the scientific discipline involved with Chemical ...
(e. g. ''
Mycobacterium ''Mycobacterium'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer ...
''). The conventional LPS-''diderm'' group of gram-negative bacteria (e.g.,
Proteobacteria Proteobacteria is a major phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plu ...
,
Aquificae The Aquificae phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a nou ...
,
Chlamydiae The Chlamydiae are a bacterial Phylum (biology), phylum and Class (biology), class whose members are remarkably diverse, including pathogens of humans and animals, symbiosis, symbionts of ubiquitous protozoa, and marine sediment forms not yet wel ...
,
Bacteroidetes The phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a noun typicall ...
,
Chlorobi The green sulfur bacteria (Chlorobiaceae) are a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of ...

Chlorobi
,
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical ...

Cyanobacteria
,
Fibrobacteres Fibrobacteres is a small bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micromet ...

Fibrobacteres
,
Verrucomicrobia Verrucomicrobia is a phylum of Gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation. They are characterized by their cell ...
,
Planctomycetes The Planctomycetes are a phylum of widely distributed bacteria, occurring in both water, aquatic and terrestrial habitats. They play a considerable role in global carbon and nitrogen cycles, with many species of this phylum capable of anaerobic amm ...
, Spirochetes,
Acidobacteria Acidobacteria is a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of ...
; "
Hydrobacteria Gracilicutes (Latin: ''gracilis'', slender, and ''cutis'', skin, referring to the cell wall) is a clade in bacterial phylogeny. Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of ...
") are uniquely identified by a few conserved signature indel (CSI) in the HSP60 (GroEL) protein. In addition, a number of bacterial Taxon, taxa (including Negativicutes, Fusobacteria, Synergistetes, and Elusimicrobia) that are either part of the phylum Firmicutes (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 a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
and that no loss of the outer membrane from any species from this group has occurred.


Example species

The proteobacteria are a major phylum of gram-negative bacteria, including ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative bacteria, Gram-negative, Facultative anaerobic organism, facultative anaer ...

Escherichia coli
'' (''E. coli''), ''Salmonella'', ''Shigella'', and other Enterobacteriaceae, ''Pseudomonas'', ''Moraxella catarrhalis, Moraxella'', ''Helicobacter'', ''Stenotrophomonas'', ''Bdellovibrio'', acetic acid bacteria, ''Legionella'' etc. Other notable groups of gram-negative bacteria include the cyanobacteria, spirochaetes, green sulfur bacteria, green sulfur, and green non-sulfur bacteria. Medically relevant gram-negative Coccus, cocci include the four types that cause a sexually transmitted disease (''Neisseria gonorrhoeae''), a meningitis (''Neisseria meningitidis''), and respiratory symptoms (''Moraxella catarrhalis'', ''Haemophilus influenzae''). Medically relevant gram-negative bacillus (shape), bacilli include a multitude of species. Some of them cause primarily respiratory problems (''Klebsiella pneumoniae'', ''Legionella pneumophila'', ''
Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bacterial differentiation. They are characterized ...
''), primarily urinary problems (''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative bacteria, Gram-negative, Facultative anaerobic organism, facultative anaer ...

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.


Bacterial transformation

Transformation (genetics), Transformation is one of three processes for horizontal gene transfer, in which exogenous genetic material passes from Bacteria, bacterium to another, the other two being bacterial conjugation, conjugation (transfer of plasmid, genetic material between two bacterial cells in direct contact) and transduction (genetics), transduction (injection of foreign DNA by a bacteriophage virus into the host bacterium). In transformation, the Nucleic acid, genetic material passes through 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''.


Role in disease

One of the several unique characteristics of gram-negative bacteria is the structure of the
bacterial outer membrane 350px, Structure of gram-negative cell envelope The bacterial outer membrane is found in gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram stain, gram-staining method of bact ...
. The outer leaflet of this membrane contains
lipopolysaccharide Lipopolysaccharides (LPS), also known as endotoxins, are large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

lipopolysaccharide
(LPS), whose
lipid A Lipid A is a lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) dissolve in water, including s, es, s, fat-soluble s ...

lipid A
portion acts as an Lipopolysaccharide, 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 a toxic reaction, resulting in fever, an increased respiratory rate, and Hypotension, low blood pressure. This is why some infections with gram-negative bacteria can lead to life-threatening
septic shock Septic shock (namely, '' infection throughout the body'') is a potentially fatal medical condition that occurs when sepsis, which is organ injury or damage in response to infection An infection is the invasion of an organism's body Tissue (b ...
. The outer membrane protects the bacteria from several
antibiotic An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system t ...
s, dyes, and
detergent A detergent is a surfactant Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting ...
s that would normally damage either the inner membrane or the cell wall (made of
peptidoglycan Peptidoglycan or murein is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repea ...

peptidoglycan
). The outer membrane provides these bacteria with resistance to
lysozyme Lysozyme, also known as muramidase or N-acetylmuramide glycanhydrolase, is an antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an ...

lysozyme
and
penicillin Penicillins (P, PCN or PEN) are a group of originally obtained from ' s, principally ' and '. Most penicillins in clinical use are chemically synthesised from naturally-produced penicillins. A number of natural penicillins have been discov ...

penicillin
. The Periplasm, periplasmic space (space between 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, Piperacillin, 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 the peri-plasmic space. Other classes of drugs that have gram negative spectrum include
cephalosporin The cephalosporins (sg. ) are a class of β-lactam antibiotics originally derived from the fungus A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeast ...
s,
monobactam Monobactams are monocyclic and bacterially-produced β-lactam antibiotics. The β-lactam A beta-lactam (β-lactam) ring is a four-membered lactam A lactam is a cyclic amide. The term is a portmanteau of the words '' lactone'' + '' amide''. ...
s (), aminoglycosides, s, macrolides, chloramphenicol, Antifolate, folate antagonists, and
carbapenem Carbapenems are a class of highly effective antibiotic An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, a ...

carbapenem
s.


Orthographic note

The adjectives ''Gram-positive'' and ''Gram-negative'' derive from the surname of Hans Christian Gram, a Danish bacteriologist; as Eponym#Orthographic conventions, eponymous adjectives, their initial letter can be either capital ''G'' or lower-case ''g'', depending on which style guide (e.g., that of the Centers for Disease Control and Prevention, CDC), if any, governs the document being written. This is further explained at ''Gram staining#Orthographic note, Gram staining § Orthographic note''.


See also

* Autochaperone * Gram stain#Gram-variable and Gram-indeterminate bacteria, Gram-variable and gram-indeterminate bacteria * Outer membrane receptor


References

*


Notes


External links


3D structures of proteins from inner membranes of Ellie Wyithe's gram-negative bacteria
{{Authority control Gram-negative bacteria, Staining Bacteriology