The genus Enterobacter belongs to the family Enterobacteriaceae. The Enterobacter genus originates primarily in the intestinal tracts of most warm-blooded animals ("entero" means intestine). The Enterobacter species is biochemically similar to Klebsiella, the key difference being that Enterobacter is ornithine positive. This genus consists of E. asburiae, E. agglomerans, E. cloacae, E. sakazakii, E. aerogenes, E. amnigenus, and E. taylorae, just to name a few.
One of the most studied Enterobacter species is E. aerogenes. The table below illustrates the biochemical characteristics of this species.
Table 1. Biochemical Characteristics of E. aerogenes.
|Methyl red||-||Gas from D-glucose||+|
|Hydrogen sulfide (TSI)||-||D-mannitol||+|
|Gelatin (22 degrees Celsius)||V||Meso-inositol||+|
V = 10 to 89.9% positive within 48 hours
(V) = more than 50% positive within 48 hours, and more than 90% positive in 3 to 7 days.
The optimal temperature for Enterobacter to grow is between 30-37 degrees Celsius. The microbe has both a respiratory and a fermentative type of metabolism. D-Glucose and other carbohydrates are catabolized with the production of acid and gas (1). Most of the carbohydrates that are fermented by Enterobacter include cellobiose, L-arabinose, D-mannitol, maltose, D-mannose, trehalose, and salicin. The microorganism is very spread out in nature. It occupies fresh water, plants, sewage, soil, and animal feces. The species inhabit the gastrointestinal tracts of warm-blooded animals. For the most part, Enterobacter is considered to be a pathogenic microorganism. The most notable species of this genus that are considered to be pathogenic are: E. sakazakii, E. cloacae, E. aerogenes, E. gergoviae, and E. agglomerans. These pathogens can cause wound, burn, and urinary tract infections and possibly meningitis and septicemia. As a rule, Klebsiella, Enterobacter, and Serratia cause infections in the same sites as does E. coli, and they are also an important cause of bacteremia. They tend to respond to broad-spectrum penicillin (ticarcillin, carbenicillin, piperacillin) and the aminoglycosides; however, since many isolates are resistant to multiple antibiotics, sensitivity studies are essential. The sensitivity of Klebsiella spp to the cephalosporins differentiates them from Enterobacter spp, which are generally resistant to these drugs. Enterobacter is also known for nitrogen fixation in soils. It is a free-living nitrogen fixer that is distributed to the soil matrix via animal feces. Theses N2-fixing microbes grow in humid environments on leaf surfaces or in leaf sheaths (phyllosphere), the soil, and root surfaces.
The above picture shows E. cloacae isolated from a lesion that was aspirated with the release of a foul-smelling gas due to gangrene.
Krieg, et al. 1993. Microbiology: Concepts and Applications. McGraw-Hill, Inc., New York.
Neal, J. L. 1995. Experiments in Soil Microbiology. Microbiology and Immunology Section, Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
Paul, E.A., and F.E. Clark. 1996. Soil Microbiology and Biochemistry, Academic Press. NY.
Information on Enterobacteriaceae.
Enterobacter sakazaki in infant formula
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