Enterobacteriaceae

Enterobacteriaceae is a large family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but one classification places it in the order Enterobacterales of the class Gammaproteobacteria in the phylum Proteobacteria.[2][3][4][5]

Not to be confused with enteric bacteria.

Enterobacteriaceae
Citrobacter freundii, one member of the family
Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Enterobacterales
Family: Enterobacteriaceae
Rahn, 1937
Genera[1]

See text

Enterobacteriaceae includes, along with many harmless symbionts, many of the more familiar pathogens, such as Salmonella, Escherichia coli, Klebsiella, and Shigella. Other disease-causing bacteria in this family include Enterobacter and Citrobacter. Members of the Enterobacteriaceae can be trivially referred to as enterobacteria or "enteric bacteria",[6] 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 the genus Enterobacter (which would be "Enterobacteraceae")—and the type genus is Escherichia.

Morphology

Members of the Enterobacteriaceae are bacilli (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 many flagella used to move about, but a few genera are nonmotile. Most members of Enterobacteriaceae have peritrichous, type I fimbriae involved in the adhesion of the bacterial cells to their hosts.

They are not spore-forming.

Metabolism

Like other proteobacteria, enterobactericeae have Gram-negative stains,[7] and they are facultative anaerobes, fermenting sugars to produce lactic acid and various other end products. Most also reduce nitrate to nitrite, although exceptions exist. Unlike most similar bacteria, enterobacteriaceae generally lack cytochrome c oxidase, although there are exceptions.

Catalase reactions vary among Enterobacteriaceae.

Ecology

Many members of this family are normal members of the gut microbiota in humans and other animals, while others are found in water or soil, or are parasites on a variety of different animals and plants.

Model organisms and medical relevance

Escherichia coli is one of the most important model organisms, and its genetics and biochemistry have been closely studied.

Some enterobacteria are important pathogens, e.g. Salmonella, or Shigella e.g. because they produce endotoxins. 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.

Genera

Validly Published Genera

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.

Candidatus Genera
  • "Candidatus Annandia"
  • "Candidatus Arocatia"
  • "Candidatus Aschnera"
  • "Candidatus Benitsuchiphilus"
  • "Candidatus Blochmannia"
  • "Candidatus Curculioniphilus"
  • "Candidatus Cuticobacterium"
  • "Candidatus Doolittlea"
  • "Candidatus Gillettellia"
  • "Candidatus Gullanella"
  • "Candidatus Hamiltonella"
  • "Candidatus Hartigia"
  • "Candidatus Hoaglandella"
  • "Candidatus Ischnodemia"
  • "Candidatus Ishikawaella"
  • "Candidatus Kleidoceria"
  • "Candidatus Kotejella"
  • "Candidatus Macropleicola"
  • "Candidatus Mikella"
  • "Candidatus Moranella"
  • "Candidatus Phlomobacter"
  • "Candidatus Profftia"
  • "Candidatus Purcelliella"
  • "Candidatus Regiella"
  • "Candidatus Riesia"
  • "Candidatus Rohrkolberia"
  • "Candidatus Rosenkranzia"
  • "Candidatus Schneideria"
  • "Candidatus Stammera"
  • "Candidatus Stammerula"
  • "Candidatus Tachikawaea"
  • "Candidatus Westeberhardia"

Proposed Genera

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.

  • Aquamonas (2009)
  • Atlantibacter (2016)
  • Superficieibacter (2018)
  • Scandinavium (2019)

Identification

To identify different genera of Enterobacteriaceae, a microbiologist may run a series of tests in the lab. These include:[8]

  • Phenol red
  • Tryptone broth
  • Phenylalanine agar for detection of production of deaminase, which converts phenylalanine to phenylpyruvic acid
  • Methyl red or Voges-Proskauer tests depend on the digestion of glucose. The methyl red tests for acid endproducts. The Voges Proskauer tests for the production of acetylmethylcarbinol.
  • Catalase test on nutrient agar tests for the production of enzyme catalase, which splits hydrogen peroxide and releases oxygen gas.
  • Oxidase test on nutrient agar tests for the production of the enzyme oxidase, which reacts with an aromatic amine to produce a purple color.
  • Nutrient gelatin tests to detect activity of the enzyme gelatinase.

In a clinical setting, three species make up 80 to 95% of all isolates identified. These are Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. However, Proteus mirabilis is now considered a part of the Morganellaceae, a sister clade within the Enterobacterales.

Antibiotic resistance
Main article: Carbapenem resistant enterobacteriaceae

Several Enterobacteriaceae strains have been isolated which are resistant to antibiotics including carbapenems, which are often claimed as "the last line of antibiotic defense" against resistant organisms. For instance, some Klebsiella pneumoniae strains are carbapenem resistant.[9]

References
  1. "List of genera included in families - Enterobacteriaceae". List of Prokaryotic Names with Standing in Nomenclature. Retrieved 26 June 2016.
  2. Don J. Brenner; Noel R. Krieg; James T. Staley (July 26, 2005) [1984 (Williams & Wilkins)]. George M. Garrity (ed.). The Gammaproteobacteria. Bergey's Manual of Systematic Bacteriology. 2B (2nd ed.). New York: Springer. p. 1108. ISBN 978-0-387-24144-9. British Library no. GBA561951.
  3. Zipcodezoo site Enterobacteriales Archived 2014-04-27 at the Wayback Machine accessed 9 Mar 2013
  4. NCBI Enterobacteriales accessed 9 Mar 2013
  5. Taxonomicon Enterobacteriales accessed 9 Mar 2013
  6. "Archived copy". Archived from the original on 2011-12-10. Retrieved 2019-01-26.CS1 maint: archived copy as title (link)
  7. "Dorlands Medical Dictionary:Enterobacteriaceae". Archived from the original on 2009-08-28.
  8. MacFaddin, Jean F. Biochemical Tests for Identification of Medical Bacteria. Williams & Wilkins, 1980, p 441.
  9. Centers for Disease Control and Prevention - Klebsiella Quotation: "Increasingly, Klebsiella bacteria have developed antimicrobial resistance, most recently to the class of antibiotics known as carbapenems."
  • Enterobacteriaceae genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
  • Evaluation of new computer-enhanced identification program for microorganisms: adaptation of BioBASE for identification of members of the family Enterobacteriaceae
  • Brown, A.E. (2009). Benson's microbiological applications: laboratory manual in general microbiology. New York: McGraw- Hill.
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