These are Gram-negative, oxidase-negative nonsporing non-acid fast straight rods (0.3-1.0 x 1.0-6.0µm). If motile they have peritrichous flagellae (except Tatumella). They are facultative anaerobes, nonhalophylic with optimal growth between 22 and 37°C. They will grow on most simple bacteriological media and most can grow on D-glucose as sole source of carbon although some require amino acids and/or vitamins. Being chemoautotrophs (able to grow on simple organic carbon and nitrogen compounds), they have both respiratory and fermentative metabolism. Both acid and gas are usually formed from glucose. The base composition of the DNA is 38-60 mol%GC. Escherichia is the type genus. An important distiguishing feature splitting the Enterobacteriaceae into two groups is the type of fermentation, either the mixed acid fermentation or the butanediol fermentation.

Genera

(1) Mixed Acid Fermentation of Sugars.

This is characteristic of the Escherichia-Salmonella-Shigella groups and is characterised by the production of acetate from pyruvate through acetyl-CoA.

Escherichia: There are currently five accepted species, E. coli , E. blattae , E. fergusonii , E. hermanii and E. vuneris.

Salmonella: There has been some controversy over the speciation of this genus; currently the species name is S. enterica, which is used for types previously considered as subspecies (subgenus) I. The other species are S. salamae (subspecies II), arizonae (subspecies IIIa), diarizonae (subspecies IIIb), houtenae (subspecies IV), bongori (subspecies V) and indica (subspecies VI). These subspecies are further subdivided into serovars.

Shigella: There are currently four accepted species, Sh. dysenteriae, Sh. flexneri, Sh. boydii and Sh. sonnei. Shigella organsms are typical members of the Enterobacteriaceae. They non-motile facultatively anaerobic Gram-negative bacilli. They are characterised by an inability to grow on synthetic media and generally weak fermentative ability against many carbohydrate substrates. They are very closely related to the Escherichia and many taxonomists suggest grouping them in that genus. The chromosomal DNA of the shigellae have a GC content of 50-52mol%.

(2) Butanediol Fermentation.

This is characteristic of the Erwinia-Enterobacter-Serratia group and characterised by the formation of butanediol as the end product of fermentation.

Erwinia:

Enterobacter: There are currently at least 13 accepted species particularly E. aerogenes , E. gergoviae , E. sakazaki and two complex groups currently known as the E. cloacae and E. agglomerans complex.

Serratia:

Genus Profiles

Escherichia

Salmonella

Shigella

Yersinia

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