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| Enterobacteriaceae | |
|---|---|
 | |
| Citrobacter freundii, one member of the family | |
Scientific classification | |
| Domain: | Bacteria |
| Kingdom: | Pseudomonadati |
| Phylum: | Pseudomonadota |
| Class: | Gammaproteobacteria |
| Order: | Enterobacterales |
| Family: | Enterobacteriaceae Rahn, 1937 |
| Genera[1] | |
See text | |
Enterobacteriaceae is a largefamily ofGram-negative bacteria. It includes over 30 genera and more than 100 species. Its classification above the level offamily is still a subject of debate, but one classification places it in the order Enterobacterales of the classGammaproteobacteria in the phylumPseudomonadota.[2][3][4][5] In 2016, the description and members of this family were emended based on comparative genomic analyses by Adeolu et al.[6]
Enterobacteriaceae includes, along with many harmlesssymbionts, many of the more familiarpathogens, such asSalmonella,Escherichia coli,Klebsiella, andShigella. Other disease-causing bacteria in this family includeEnterobacter andCitrobacter. Members of the Enterobacteriaceae can betrivially referred to as enterobacteria or "enteric bacteria",[7] as several members live in the intestines of animals. In fact, the etymology of the family is enterobacterium with the suffix to designate a family (aceae)—not after thegenusEnterobacter (which would be "Enterobacteraceae")—and the type genus isEscherichia.
Members of the Enterobacteriaceae arebacilli (rod-shaped), and are typically 1–5 μm in length. They typically appear as medium to large-sized grey colonies on blood agar, although some can express pigments.
Most have manyflagella used to move about, but a few genera are nonmotile. Most members of Enterobacteriaceae have peritrichous, type Ifimbriae involved in the adhesion of the bacterial cells to their hosts.[8]
Like other Pseudomonadota, Enterobacteriaceae haveGram-negative stains,[10] and they arefacultative anaerobes, somefermenting sugars to producelactic acid and various other end products. Most also reducenitrate tonitrite, although exceptions exist. Unlike most similar bacteria, Enterobacteriaceae generally lackcytochrome c oxidase, there are exceptions.
Catalase reactions vary among Enterobacteriaceae.
Many members of this family are normal members of thegut microbiota in humans and other animals,[11] while others are found in water or soil, or areparasites on a variety of different animals and plants.[12][13]
Escherichia coli is one of the most importantmodel organisms, and itsgenetics andbiochemistry have been closely studied.[14]
Some enterobacteria are important pathogens, e.g.Salmonella, orShigella e.g. because they produceendotoxins.[15] Endotoxins reside in the cell wall and are released when the cell dies and the cell wall disintegrates. Some members of the Enterobacteriaceae produce endotoxins that, when released into the bloodstream following cell lysis, cause a systemic inflammatory and vasodilatory response. The most severe form of this is known as endotoxic shock, which can be rapidly fatal.
Enterobacteriaceae was originally the sole family under the order Enterobacteriales. The family contained a large array of biochemically distinct species with different ecological niches, which made biochemical descriptions difficult.[16][17] The original classification of species to this family and order was largely based on 16S rRNA genome sequence analyses, which is known to have low discriminatory power and the results of which changes depends on the algorithm and organism information used. Despite this, the analyses still exhibited polyphyletic branching, indicating the presence of distinct subgroups within the family.[18]
In 2016, the order Enterobacteriales was renamed to Enterobacterales, and divided into 7 new families, including the emended Enterobacteriaceae family.[6] This emendation restricted the family to include only those genera directly related to the type genus, which included most of the enteric species under the order. This classification was proposed based on the construction of several robust phylogenetic trees using conserved genome sequences, 16S rRNA sequences and multilocus sequence analyses. Molecular markers, specifically conserved signature indels, specific to this family were identified as evidence supporting the division independent of phylogenetic trees.
In 2017, a subsequent study using comparative phylogenomic analyses identified the presence of 6 subfamily level clades within the family Enterobacteriaceae, namely the "Escherichia clade", "Klebsiella clade", "Enterobacter clade", "Kosakonia clade", "Cronobacter clade", "Cedecea clade" and an "Enterobacteriaceae incertae sedis clade" containing species whose taxonomic placement within the family is unclear.[19] However, this division was not officially proposed as the subfamily rank is generally not used.
Analyses of genome sequences from Enterobacteriaceae species identified 21conserved signature indels (CSIs) that are uniquely present in this family in the proteinsNADH:ubiquinone oxidoreductase (subunit M), twitching motility protein PilT, 2,3-dihydroxybenzoate-AMP ligase, ATP/GTP-binding protein, multifunctional fatty acid oxidation complex (subunit alpha),S-formylglutathione hydrolase,aspartate-semialdehyde dehydrogenase,epimerase,membrane protein, formate dehydrogenylase (subunit 7),glutathione S-transferase, major facilitator superfamily transporter,phosphoglucosamine mutase, glycosyl hydrolase 1 family protein, 23S rrna [uracil(1939)-C(5)]-methyltransferase, co-chaperone HscB,N-acetylmuramoyl-L-alanine amidase, sulfate ABC transporter ATP-binding protein CysA, and LPS assembly protein LptD.[6] These CSIs provide a molecular means of distinguishing Enterobacteriaceae from other families within the order Enterobacterales and other bacteria.
The following genera have been validly published, thus they have "Standing in Nomenclature". The year the genus was proposed is listed in parentheses after the genus name.
The following genera have been effectively, but not validly, published, thus they do not have "Standing in Nomenclature". The year the genus was proposed is listed in parentheses after the genus name.
To identify differentgenera of Enterobacteriaceae, a microbiologist may run a series of tests in the lab. These include:[20]
In a clinical setting, three species make up 80 to 95% of all isolates identified. These areEscherichia coli,Klebsiella pneumoniae, andProteus mirabilis. However,Proteus mirabilis is now considered a part of theMorganellaceae, a sister clade within theEnterobacterales.
Several Enterobacteriaceae strains have been isolated which areresistant to antibiotics includingcarbapenems, which are often claimed as "the last line of antibiotic defense" against resistant organisms. For instance, someKlebsiella pneumoniae strains are carbapenem resistant.[21] Various carbapenemases genes (blaOXA-48, blaKPC and blaNDM-1, blaVIM and blaIMP) have been identified in carbapenem resistant Enterobacteriaceae includingEscherichia coli andKlebsiella pneumoniae.[22]
Increasingly, Klebsiella bacteria have developedantimicrobial resistance, most recently to the class of antibiotics known as carbapenems.
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