The Enterobacteriaceae are a large family of Gram-negative bacteria that 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.
This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria
in the phylum Proteobacteria.
Phylogenetically, in the Enterobacteriales, several peptidoglycan-less insect endosymbionts
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.
Members of the Enterobacteriaceae can be trivially referred to as enterobacteria or "enteric
bacteria", 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 — not
after the genus Enterobacter— and the type genus is Escherichia.
Characteristics Members of the Enterobacteriaceae are rod-shaped,
and are typically 1-5 μm in length.
They appear as small grey colonies on blood agar.
Like other proteobacteria, enterobacteria have Gram-negative stains, 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, enterobacteria generally lack cytochrome C oxidase, although
there are exceptions.
Most have many flagella used to move about, but a few genera are nonmotile.
They are not spore-forming.
Catalase reactions vary among Enterobacteriaceae.
Many members of this family are a normal part of the gut flora found in the intestines of
humans and other animals, while others are found in water or soil, or are parasites on
a variety of different animals and plants.
Escherichia coli is one of the most important model organisms, and its genetics and biochemistry
have been closely studied.
Most members of Enterobacteriaceae have peritrichous, type I fimbriae involved in the adhesion of
the bacterial cells to their hosts.
Some enterobacteria produce endotoxins.
Endotoxins reside in the cell cytoplasm and are released when the cell dies and the cell
wall disintegrates.
Some members of the Enterobacteriaeceae 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.
Identification To identify different genera of Enterobacteriaceae,
a microbiologist may run a series of tests in the lab.
These include: 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 catalase enzyme, 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.
Antibiotic resistance
Several Enterobacteriacea strains have been isolated which are resistant to antibiotics
including carbapenem, which are often claimed as "the last line of antibiotic defense" against
resistant organisms.
For instance, some Klebsiella pneumonia strains are carbapenem resistant.
Examples/classification The following inexhaustive list details bacterial
genera classified as members of Enterobacteriaceae.
Genera Alishewanella
Alterococcus Aquamonas
Aranicola Arsenophonus
Azotivirga Blochmannia
Brenneria Buchnera
Budvicia Buttiauxella
Cedecea Citrobacter
Cronobacter Dickeya
Edwardsiella Enterobacter
Erwinia, e.g. Erwinia amylovora, Erwinia tracheiphila, Erwinia carotovora, etc.
Escherichia, e.g. Escherichia coli Ewingella
Grimontella Hafnia
Hamiltonella Klebsiella, e.g. Klebsiella pneumoniae
Kluyvera Leclercia
Leminorella Moellerella
Morganella Obesumbacterium
Pantoea Pectobacterium see Erwinia
Candidatus Phlomobacter Photorhabdus, e.g. Photorhabdus luminescens
Plesiomonas, e.g. Plesiomonas shigelloides Pragia
Proteus, e.g. Proteus vulgaris Providencia
Rahnella Regiella
Raoultella Salmonella
Samsonia Serratia, e.g. Serratia marcescens
Shigella Sodalis
Tatumella Trabulsiella
Wigglesworthia Xenorhabdus
Yersinia, e.g. Yersinia pestis Yokenella
References
External links 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 [1]
Brown, A.E..
Benson's microbiological applications: laboratory manual in general microbiology.
New York: McGraw- Hill.