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Citrobacter freundii.jpg
Citrobacter freundii , one member of the family
Scientific classification Red Pencil Icon.png
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Enterobacteriales
Rahn, 1937
Genera [1]

See text

The Enterobacteriaceae are a large family of Gram-negative bacteria. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the phylum Proteobacteria. [2] [3] [4] [5]

Family is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy; it is classified between order and genus. A family may be divided into subfamilies, which are intermediate ranks between the ranks of family and genus. The official family names are Latin in origin; however, popular names are often used: for example, walnut trees and hickory trees belong to the family Juglandaceae, but that family is commonly referred to as being the "walnut family".

Gram-negative bacteria group of bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation

Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the gram-staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall sandwiched between an inner cytoplasmic cell membrane and a bacterial outer membrane.

Gammaproteobacteria class of bacteria

Gammaproteobacteria are a class of bacteria. Several medically, ecologically, and scientifically important groups of bacteria belong to this class. Like all Proteobacteria, the Gammaproteobacteria are Gram-negative.


Enterobacteriaceae includes, along with many harmless symbionts, many of the more familiar pathogens, such as Salmonella , Escherichia coli , Yersinia pestis , Klebsiella , and Shigella . Other disease-causing bacteria in this family include Proteus , Enterobacter , Serratia , and Citrobacter . Phylogenetically, in the Enterobacteriales, several peptidoglycan-less insect endosymbionts[ citation needed ] form a sister clade to the Enterobacteriaceae, but as they are not validly described, this group is not officially a taxon; examples of these species are Sodalis , Buchnera , Wigglesworthia , Baumannia cicadellinicola , and Blochmannia , but not former Rickettsias. [6] Members of the Enterobacteriaceae can be trivially 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 the genus Enterobacter (which would be "Enterobacteraceae")—and the type genus is Escherichia .

Symbiosis type of a close and long-term biological interaction between two different biological organisms

Symbiosis is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic. The organisms, each termed a symbiont, may be of the same or of different species. In 1879, Heinrich Anton de Bary defined it as "the living together of unlike organisms". The term was subject to a century-long debate about whether it should specifically denote mutualism, as in lichens; biologists have now abandoned that restriction.

Pathogenic bacteria

Pathogenic bacteria are bacteria that can cause disease. This article deals with human pathogenic bacteria. Although most bacteria are harmless or often beneficial, some are pathogenic, with the number of species estimated as fewer than a hundred that are seen to cause infectious diseases in humans. By contrast, several thousand species exist in the human digestive system.

<i>Salmonella</i> Genus of prokaryotes

Salmonella is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of Salmonella are Salmonella enterica and Salmonella bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes.


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 (such as Serratia marcescens).

Bacillus (shape) rod-shaped bacterium (not to be confused with the taxon Bacilli)

A bacillus or bacilliform bacterium is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name Bacillus, capitalized and italicized, refers to a specific genus of bacteria. The name Bacilli, capitalized but not italicized, can also refer to a less specific taxonomic group of bacteria that includes two orders, one of which contains the genus Bacillus. When the word is formatted with lowercase and not italicized, 'bacillus', it will most likely be referring to shape and not to the genus at all. Bacilliform bacteria are also often simply called rods when the bacteriologic context is clear. Sea Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades.

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.

Fimbria (bacteriology)

In bacteriology, a fimbria, also referred to as an "attachment pilus" by some scientists, is an appendage that can be found on many Gram-negative and some Gram-positive bacteria that is thinner and shorter than a flagellum. This appendage ranges from 3-10 nanometers in diameter and can be up to several micrometers long. Fimbriae are used by bacteria to adhere to one another and to adhere to animal cells and some inanimate objects. A bacterium can have as many as 1,000 fimbriae. Fimbriae are only visible with the use of an electron microscope. They may be straight or flexible.

They are not spore-forming.


Like other proteobacteria, enterobactericeae have Gram-negative stains, [8] 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 (e.g. Photorhabdus ). Unlike most similar bacteria, enterobacteriaceae generally lack cytochrome C oxidase, although there are exceptions (e.g. Plesiomonas shigelloides ).

Lactic acid group of stereoisomers

Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)CO2H. It is white in solid state and it is extremely soluble in water. Solubility is so high that 1 part of lactic acid can dissolve 12 parts of water. While in liquid state (dissolved state) it is a colorless solution. Production includes both artificial synthesis as well as natural sources. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of carboxyl group adjacent to the hydroxyl group. It is used as a synthetic intermediate in many organic synthesis industries and in various biochemical industries. The conjugate base of lactic acid is called lactate.

Nitrate anion

Nitrate is a polyatomic ion with the molecular formula NO
and a molecular mass of 62.0049 u. Organic compounds that contain the nitrate ester as a functional group (RONO2) are also called nitrates.

Nitrite anion

The nitrite ion, which has the chemical formula NO
, is a symmetric anion with equal N–O bond lengths. Upon protonation, the unstable weak acid nitrous acid is produced. Nitrite can be oxidized or reduced, with the product somewhat dependent on the oxidizing/reducing agent and its strength. The nitrite ion is an ambidentate ligand, and is known to bond to metal centers in at least five different ways. Nitrite is also important in biochemistry as a source of the potent vasodilator nitric oxide. In organic chemistry the NO
group is present in nitrous acid esters and nitro compounds. Nitrite is also used in the food production industry for curing meat.

Catalase reactions vary among Enterobacteriaceae.


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.

Gut flora community of microorganisms in the gut

Gut flora, or gut microbiota, or gastrointestinal microbiota, is the complex community of microorganisms that live in the digestive tracts of humans and other animals, including insects. The gut metagenome is the aggregate of all the genomes of gut microbiota. The gut is one niche that human microbiota inhabit.

Parasitism Interaction between two organisms living together in more or less intimate association in a relationship in which association is disadvantageous or destructive to one of the organisms

In evolutionary biology, parasitism is a relationship between species, where one organism, the parasite, lives on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has characterised parasites as "predators that eat prey in units of less than one". Parasites include protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes. There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration, directly transmitted parasitism, trophically transmitted parasitism, vector-transmitted parasitism, parasitoidism, and micropredation.

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, Shigella, or Yersinia, 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.





  • Aquamonas
  • Aranicola
  • Atlantibacter
  • Chania
  • Grimontella
  • Guhaiyinggella
  • Margalefia
  • Tiedjeia


To identify different genera of Enterobacteriaceae, a microbiologist may run a series of tests in the lab. These include: [9]

In a clinical setting, three species make up 80 to 95% of all isolates identified. These are Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis.

Antibiotic resistance

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. [10]

Related Research Articles

Agar plate

An agar plate is a Petri dish that contains agar as a solid growth medium plus nutrients, used to culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics.

<i>Klebsiella pneumoniae</i> species of bacterium

Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar.

<i>Proteus</i> (bacterium) genus of bacteria

Proteus is a genus of Gram-negative Proteobacteria. Proteus bacilli are widely distributed in nature as saprophytes, being found in decomposing animal matter, sewage, manure soil, the mammalian intestine, and human and animal feces. They are opportunistic pathogens, commonly responsible for urinary and septic infections, often nosocomial.

MacConkey agar culture medium used in microbiology

MacConkey agar is an indicator, a selective and differential culture medium for bacteria designed to selectively isolate Gram-negative and enteric bacilli and differentiate them based on lactose fermentation. The crystal violet and bile salts inhibit the growth of Gram-positive organisms which allows for the selection and isolation of gram-negative bacteria. Enteric bacteria that have the ability to ferment lactose can be detected using the carbohydrate lactose, and the pH indicator neutral red.

Carbapenem group of β-lactam antibiotics

Carbapenems are a class of highly effective antibiotic agents commonly used for the treatment of severe or high-risk bacterial infections. This class of antibiotics is usually reserved for known or suspected multidrug-resistant (MDR) bacterial infections. Similar to penicillins and cephalosporins, carbapenems are members of the beta lactam class of antibiotics, which kill bacteria by binding to penicillin-binding proteins, thus inhibiting bacterial cell wall synthesis. However, these agents individually exhibit a broader spectrum of activity compared to most cephalosporins and penicillins. Furthermore, carbapenems are typically unaffected by emerging antibiotic resistance, even to other beta-lactams.

Marbofloxacin chemical compound

Marbofloxacin is a carboxylic acid derivative third generation fluoroquinolone antibiotic. It is used in veterinary medicine under the trade names Marbocyl,Forcyl and Zeniquin. A formulation of marbofloxacin combined with clotrimazole and dexamethasone is available under the name Aurizon.

The indole test is a biochemical test performed on bacterial species to determine the ability of the organism to convert tryptophan into indole. This division is performed by a chain of a number of different intracellular enzymes, a system generally referred to as "tryptophanase."

Enrofloxacin chemical compound

Enrofloxacin (ENR) is a fluoroquinolone antibiotic sold by the Bayer Corporation under the trade name Baytril. Enrofloxacin is currently approved by the FDA for the treatment of individual pets and domestic animals in the United States. In September 2005, the FDA withdrew approval of Baytril for use in water to treat flocks of poultry, as this practice was noted to promote the evolution of fluoroquinolone-resistant strains of the bacterium Campylobacter, a human pathogen.

Ceftibuten chemical compound

Ceftibuten is a third-generation cephalosporin antibiotic. It is an orally administered agent, with two dosage forms, capsule or oral suspension. It is marketed by Pernix Therapeutics under the trade name Cedax.

Swarming motility rapid and coordinated translocation of a bacterial population across solid or semi-solid surfaces

Swarming motility is a rapid and coordinated translocation of a bacterial population across solid or semi-solid surfaces, and is an example of bacterial multicellularity and swarm behaviour. Swarming motility was first reported by Jorgen Henrichsen and has been mostly studied in genus Serratia, Salmonella, Aeromonas, Bacillus, Yersinia, Pseudomonas, Proteus, Vibrio and Escherichia.

Voges–Proskauer or VP is a test used to detect acetoin in a bacterial broth culture. The test is performed by adding alpha-naphthol and potassium hydroxide to the Voges-Proskauer broth which has been inoculated with bacteria. A cherry red color indicates a positive result, while a yellow-brown color indicates a negative result.

Viable but nonculturable

Viable but nonculturable (VBNC) bacteria refers to bacteria that are in a state of very low metabolic activity and do not divide, but are alive and have the ability to become culturable once resuscitated.

Carbapenem-resistant Enterobacteriaceae (CRE) or carbapenemase-producing Enterobacteriaceae (CPE) are Gram-negative bacteria that are resistant to the carbapenem class of antibiotics, considered the drugs of last resort for such infections. They are resistant because they produce an enzyme called a carbapenemase that disables the drug molecule. The resistance can vary from moderate to severe. Enterobacteriaceae are common commensals and infectious agents. Experts fear CRE as the new "superbug". The bacteria can kill up to half of patients who get bloodstream infections. Tom Frieden, former head of the Centers for Disease Control and Prevention has referred to CRE as "nightmare bacteria". Types of CRE are sometimes known as KPC and NDM. KPC and NDM are enzymes that break down carbapenems and make them ineffective. Both of these enzymes, as well as the enzyme VIM have also been reported in Pseudomonas.

Dow Corning added silane (SiH4) to quaternary ammonia compounds, to improve the adhesion of QUATs to a variety of surfaces. In doing so, Dow invented a durable class of antimicrobials that are effective against a range of unicellular organisms.


Ceftolozane is a novel cephalosporin antibiotic, developed for the treatment of infections with gram-negative bacteria that have become resistant to conventional antibiotics. It was studied for urinary tract infections, intra-abdominal infections and ventilator-associated bacterial pneumonia. Ceftolozane is combined with the β-lactamase inhibitor tazobactam, which protects ceftolozane from degradation. Ceftolozane-tazobactam is indicated for the treatment of complicated urinary tract infections and complicated intra abdominal infections.

Tevenvirinae is a subfamily of viruses in the order Caudovirales, in the family Myoviridae. Bacteria and archaea serve as natural hosts. There are currently 54 species in this subfamily, most included in 11 genera.


  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. Williams, K. P.; Gillespie, J. J.; Sobral, B. W. S.; Nordberg, E. K.; Snyder, E. E.; Shallom, J. M.; Dickerman, A. W. (2010). "Phylogeny of Gammaproteobacteria". Journal of Bacteriology. 192 (9): 2305–2314. doi:10.1128/JB.01480-09. PMC   2863478 . PMID   20207755.
  7. "Archived copy". Archived from the original on 2011-12-10. Retrieved 2019-01-26.CS1 maint: Archived copy as title (link)
  8. "Dorlands Medical Dictionary:Enterobacteriaceae".
  9. MacFaddin, Jean F. Biochemical Tests for Identification of Medical Bacteria. Williams & Wilkins, 1980, p 441.
  10. 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."