Enterobacteriaceae

Enterobacteriaceae is a large  group 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.

  Scientific classification

Domain:Bacteria

Phylum:proteobacteria

Class:Gammaproteobacteria

Order:Enterobacterales

Family:Enterobacteriaceae

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"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 Eshcherichia.

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 fimbrea 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,and they are facultative anarobes, farmenting 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 oxidase, although there are exceptions.

Catalase reactions vary among Enterobacteriaceae.

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 pneumonia strains are carbapenem resistant.

IdentificationEdit

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

• d Phenol red

• Tryptone broth

•  phenylalanine agar for detection of production of deaminase, which converts phenylalanine to phenylpyruvic acid

•  Methyl red or Voges-Proskauer test 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.

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