Enterobacteriaceae

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Enterobacteriaceae
Escherichia coli (secondary electron microscope image, subsequently colored)

Escherichia coli (secondary electron microscope image, subsequently colored)

Systematics
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Gammaproteobacteria
Order : Enterobacteria (Enterobacterales)
Family : Enterobacteriaceae
Scientific name
Enterobacteriaceae
Rahn emend in 1937 . Adeolu et al. 2016

The Enterobacteriaceae are a large group of gram-negative bacteria . According to the phylogenetic system , they belong to the order of Enterobacterales in the class of Gammaproteobacteria in the division ( Divisio , also known as Phylum among prokaryotes ) Proteobacteria and form their own family there . The name Enterobacteriaceae is derived from enteron ( ancient Greek ἕντερον 'intestine'), because many of them are typical intestinal inhabitants . However, many free- living and ubiquitous , non-colon-dwelling bacterial species also belong to this family.

Until 2016 the Enterobacteriaceae were the only family in the order "Enterobacteriales", but the name of this order was not valid according to the rules of the Bacteriological Code (ICBN). In 2016, phylogenetic methods led to the establishment of the order Enterobacterales (Enterobacteria), combined with a division of the previously known taxa into several new families. The new system means that fewer genera belong to the Enterobacteriaceae family and that known genera from the same order as Yersinia , Proteus or Hafnia are placed in other families (see section Systematics and Taxonomy ).

features

Appearance

The cells are rod-shaped and usually 1 to 5  µm long and about 0.5-1.0 µm in diameter. No endospores are formed. Most of them can actively move with flagella , they are motile , but there are also species that cannot move actively, e.g. B. Klebsiella and Raoultella . Since the cell wall consists of a few murein layers and a second, outer membrane of phospholipids and lipopolysaccharides , the Enterobacteriaceae are gram-negative .

metabolism

Raoultella planticola in SIM agar with a negative result for H 2 S formation, with a negative result for the indole test and with a negative result for motility .

Their metabolism is facultatively anaerobic , so they can break down substances through oxidation in the presence of oxygen , and ferment under anoxic conditions (no oxygen) . In the Enterobacteriaceae, the catalase test is positive and the oxidase test is negative. Two important anaerobic metabolic pathways which are used to differentiate the individual species are the 2,3-butanediol fermentation and the mixed acid fermentation ( mixed acid fermentation ). In mixed acid fermentation, the end products and by-products are mainly acids such as acetic acid , lactic acid and succinic acid (succinate), but no butanediol . In 2,3-butanediol fermentation, the fermentation of glucose results in smaller amounts of acids as end products and by-products, but above all in large amounts the alcohol 2,3-butanediol . Another characteristic of 2,3-butanediol fermentation is the intermediate product acetoin and the much higher gas production ( CO 2 ). One finds butanediol fermentation z. B. Enterobacter and Klebsiella . Use mixed acid fermentation u. a. Genera such as Citrobacter , Escherichia , Salmonella and Shigella .

A large number of biochemical diagnostic tests are used to determine the individual genera . For example, the intermediate product acetoin of 2,3-butanediol fermentation is detected with the help of the Voges-Proskauer test . This reaction is part of the so-called IMViC test procedure to distinguish Escherichia from other Enterobacteriaceae. Since colored reaction products are often produced in the test procedure or pH indicators with a color change are used, they are referred to in the laboratory as the colorful series . The detection of the enzyme β-galactosidase is also often used to differentiate the representatives of the Enterobacteriaceae. Bacteria that have this enzyme can hydrolytically split the disaccharide lactose (milk sugar) into the monosaccharides glucose and galactose in order to use them in the metabolism.

Phylogenetics

→ See also: Section Systematics and Taxonomy in the article of the order Enterobacterales

By using phylogenetic methods, the tribal history and the relationships between the bacteria can be clarified. In the description of the order Enterobacterales Adeolu et al. In 2016 and the families belonging to it, the Enterobacteriaceae form a monophyletic group in a phylogenetic tree (based on genome and genetic analyzes ) . Furthermore, 21, conserved characteristic indels (Engl. ' Conserved signature inserts and deletions CSI) set, which are typical of the representatives of the family, but do not occur in the other bacteria of the order.

Occurrence

Many Enterobacteriaceae are part of the healthy intestinal flora of humans and animals; however, they also occur everywhere in the environment (soil, water). Some are pathogens in humans and animals. They often occur as nosocomial pathogens ("hospital germs") and attack people with a weak immune system . Probably the most important member of the family is Escherichia coli , one of the most important model organisms in genetics , biochemistry and microbiology .

Systematics and taxonomy

External system

The order of Enterobacterales established in 2016 includes eight families (including the Hafniaceae , Morganellaceae and Yersiniaceae ) with a total of around 60 genera. The type genus of the order that has been newly established and thus corresponds to the rules of the bacteriological code (ICBN) is the genus Enterobacter .

Internal system

Light microscopic picture of Citrobacter freundii after Gram staining

The type genus of the family is the genus Escherichia , while the genus Enterobacter has been established as the type genus of the order Enterobacterales. The following genera belong to the Enterobacteriaceae family (as of 2019):

Colonies of Cronobacter sakazakii on a nutrient medium
Colonies of Salmonella on XLD agar with positive results for H 2 S formation

Synonyms and not reliably assigned taxa

All species from Levinea Young et al. 1971 Werkman and Gillen 1932 were added to the genus Citrobacter . The species Calymmatobacterium granulomatis was reclassified as Klebsiella granulomatis in 1999 .

"Atlantibacter", "Edaphovirga", "Kosakonia", "Lelliottia", "Limnobaculum", "Pluralibacter", "Pseudocitrobacter", "Rosenbergiella", "Siccibacter" and "Superficieibacter" are other genera whose names are not (yet) available is recognized according to the rules of the Bacteriological Code (ICBN) (as of 2019) and of whom it is suspected that they are part of the family. There are also other genera or species with the status Candidatus that can be regarded as belonging to the family. These are, for example, " Candidatus Arocatia carayoni", " Candidatus Ishikawaella capsulata" and " Candidatus Schneideria nysicola".

etymology

The name of the genus Enterobacter Hormaeche and Edwards 1960 derives from enteron ( ancient Greek ἕντερον 'intestine') and the Latinized word bacter for ancient Greek βακτηρΐα 'rod', consequently means something like "small rod bacterium in the intestine". The name of the Enterobacteriaceae Rahn 1937 family contains the same word stems, but the origin of the name is not known for certain by Rahn as the first person to describe it. At the time of its description, the bacteria of the genus Enterobacter were not yet named by this name. In the first edition of Bergey's Manual of Systematic Bacteriology from 1984, the etymology is presented as follows: The Latinized word enterobacterium means 'intestinal bacteria', with the typical ending -aceae to identify a family, the name Enterobacteriaceae means “family of intestinal bacteria”. This derivation would explain why the name is Enterobacteriaceae (with an additional "i") and not Enterobacteraceae.

Reporting requirement

In Switzerland, the positive laboratory analytical finding is carbapenemase visual Enterobacteriaceae reporting requirements for doctors, hospitals, etc. or laboratories namely by following the Epidemics Act (EpG) in connection with the epidemic Regulation and Annex 1 and Annex 3 of the Regulation of the EDI for reporting Observations of communicable diseases in humans .

See also

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literature

Individual evidence

  1. ↑ a b c d e M. Adeolu, S. Alnajar, S. Naushad, RS Gupta: Genome-based phylogeny and taxonomy of the 'Enterobacteriales': proposal for Enterobacterales ord. nov. divided into the families Enterobacteriaceae, Erwiniaceae fam. nov., Pectobacteriaceae fam. nov., Yersiniaceae fam. nov., Hafniaceae fam. nov., Morganellaceae fam. nov., and Budviciaceae fam. nov. In: International Journal of Systematic and Evolutionary Microbiology. No. 66 , December 2016, p. 5575-5599 , doi : 10.1099 / ijsem.0.001485 .
  2. ↑ a b Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 3-8274-0566-1 , pp. 531-536.
  3. ↑ a b Jean Euzéby, Aidan C. Parte: Classification of domains and phyla - Hierarchical classification of prokaryotes (bacteria). In: List of Prokaryotic names with Standing in Nomenclature, Systematics of Bacteria (LPSN) . Retrieved December 21, 2019 .
  4. ↑ Taxonomy Browser Enterobacteriaceae. In: National Center for Biotechnology Information (NCBI) website . Retrieved December 21, 2019 .
  5. ^ E. Hormaeche, PR Edwards: A proposed genus Enterobacter. In: International Bulletin of Bacteriological Nomenclature and Taxonomy. Volume 10, No. 2, April 1960, pp. 71-74. ISSN  0096-266X . doi : 10.1099 / 0096266X-10-2-71 .
  6. ^ Jean Euzéby, Aidan C. Parte: Genus Enterobacter. In: List of Prokaryotic names with Standing in Nomenclature, Systematics of Bacteria (LPSN) . Retrieved December 21, 2019 .
  7. ^ Jean Euzéby, Aidan C. Parte: Familiy Enterobacteriaceae. In: List of Prokaryotic names with Standing in Nomenclature, Systematics of Bacteria (LPSN) . Retrieved December 21, 2019 .

Web links

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