ENTEROBACTER

15 plus species including:

SPECIES

Enterobacter aerogenes
Enterobacter agglomerans
Enterobacter amnigenus
Enterobacter asburiae
Enterobacter cancerogenus
Enterobacter cloacae
Enterobacter dissolvens
Enterobacter gergoviae
Enterobacter hormaechei
Enterobacter intermedium
Enterobacter nimipressuralis
Enterobacter sakazakii
Enterobacter taylorae

MICROSCOPIC APPEARANCE

Gram Stains: Negative.
Morphology: Straight rods.
Size: 0.6-1.0 micrometers by 1.2-3.0 micrometers.
Motility: Some are motile by four to six peritrichous flagella.
Spores: No.

MACROSCOPIC APPEARANCE

Enterobacter spp. grow rapidly on the usual enteric media. In general, the strains from environmental sources grow better at 20-30 degrees C., whereas strains from clinical sources grow better at 37 degrees C. Colonial morphology differs greatly among Enterobacter spp. ranging from smooth, irregularly round to rough "cauliflower" type colonies. Anaerogenic strains often exhibit yellow pigmented colonies.

METABOLIC PROPERTIES

Aerobic; Facultatively anaerobic. Chemoorganotrophic. Both respirative and fermentative. Glucose is fermented with the production of acid and gas.

KEY BIOCHEMICAL REACTIONS

Note: Some environmental strains give erratic biochemical reactions at 37 degrees C.

HABITAT

All species are found in the natural environment including water, sewage, soil, plants, human and animal feces. E. cloacae is the most frequently isolated Enterobacter species form man and animals. It is found in human and animal feces. Several species have been isolated from urine, sputum and the respiratory tract, pus, and occasionally from blood or spinal fluid.

PATHOGENICITY

Several species, most notable E. cloacae , E. sakazakii , E. aerogenes , E. agglomerans and E. gergoviae , are opportunistic pathogens of animals and humans; they are not considered to enteric pathogens. Enterobacter species are often implicated in burn, wound, and urinary tract infections. They occasionally cause septicemia and meningitis. E. sakazakii is often commensal without clinical significance and is occasionally a pathogen causing neonatal meningitis and bacteremia. E. agglomerans can behave as an opportunistic pathogen in immunologically compromised patients such as neonates, premature infants, burned or multiply traumatized patients, and patients with leukemia or who are undergoing immunosuppressive therapy. This species is also isolated by blood culture because they are generally introduced by such invasive procedures as catheterization and intubation. Such contaminations result in transitory bacteremia and occasionally septicemia. E. gergoviae have been implicated in a long-term nosocomial outbreak of urinary tract infections. Other species, such as E. amnigenius and E. intermedium have not been isolated from human infection.

RECOMMENDED MEDIA

For culture: Blood Agar 5%, TSA Agar, Nutrient Agar.
For selective isolation: MacConkey Agar, Hektoen Enteric (HE) Agar, EMB Agar.
For maintenance: Blood Agar 5%, TSA Agar, Nutrient Agar.

INCUBATION

Temperature: 35 degrees C. (Environmental strains may grow better at 20-30 degrees C.)
Time: 16-18 hours.
Atmosphere: Aerobic (facultative anaerobe).

REFERENCES

1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P. R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.


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