General Overview
Enterobacter species are opportunistic pathogens associated with many infections such as urinary tract infections, wound infections, and septicaemia.
Mainly people with compromised immunity get these infections.
Enterobacter species can be found in the human intestinal tract as well as in animal intestinal tract.
Moreover, they can be found in soil, sewage, water, and dairy products.
Many features of this species are common with those of Klebsiella species.
However, they can be distinguished by the motility of Enterobacter.
The clinically important Enterobacter species is Enterobacter cloacae (E. cloacae).
Enterobacter agglomerans (E. agglomerans) and Enterobacter anaerogenic (E. anaerogenic) are also found occasionally.
Enterobacter amnigenus (E. amnigenus) and Enterobacter asburiae (E. asburiae) are also cause human diseases.  Â
Microscopy
Gram negative bacilli can be seen in Gram-stained smears. Motile in wet preparations.
Culture
They are aerobes and facultative anaerobes.
Blood agar
This organism produces large colonies. However, they are not so mucoid like Klebsiella colonies.
They are slightly mucoid. They are gray white in colour.
MacConkey agar
Produce lactose fermenting pink red colonies on MacConkey agar. They are slightly mucoid colonies.
CLED agar
Produce yellow colour slightly mucoid colonies on CLED agar medium.
EMB agar
Produce large, mucoid, pink to purple colonies with no metallic green sheen
- Urease negative
- VP positive (Voges-Proskauer,)
- ONPG positive (beta-galactosidase)
- Ferment Lactose, Mannitol, Glucose
- Different strains give different results in sucrose fermentation
- Oxidase negative
- Citrate positive. But some minority of strains are oxidase negative
- Indole negative
- Lysine decarboxylase test, different stains give different results
- In KIA medium Enterobacter species give Yellow butt, yellow slant with gas and do not produce H2S (Hydrogen sulphide)
Serotyping and phage typing of Enterobacter has developed according to the O and H antigens. In out breaks, characterization of strains has been done by using pulsed-field gel electrophoresis.
Treatment
Production of chromosomal β-lactamase with cephalosporinase can be seen in Enterobacter.
Therefore, they are highly resistant to Penicillins and many cephalosporins. Many strains are also resistant to antibiotic such as tetracyclines, chloramphenicol and streptomycin.
However, infections can be treated by aminoglycosides including gentamicin. Enterobacter also sensitive to polymyxins.Â
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