ESCHERICHIA

SPECIES

Escherichia adecarboxylata
Escherichia blattae
Escherichia coli
Escherichia fergusonii
Escherichia hermannii
Escherichia vulneris

MICROSCOPIC APPEARANCE

Gram Stains: Gram-negative.
Morphology: Straight rods.
Size: 1.1-1.5 micrometers by 2.0-6.0 micrometers.
Motility: Escherichia spp. are motile by peritrichous flagella or are non-motile. In addition to flagella, most strains have fimbriae (pili) that extend from the bacterial surface into the surrounding medium. Some fimbriae have specific functions as adhesive organs.
Capsules: Capsules or microcapsules occur in many strains.
Spores: None.
Other: They occur singly or in pairs.

MACROSCOPIC APPEARANCE

Most colonies generally appear smooth, low convex, moist and gray with a shiny surface and an entire edge. They may be rough dry and difficult to disperse in saline. There are intermediate forms between these extremes. Mucoid and slime producing forms occur.

METABOLIC APPEARANCE

Respiratory; fermentative; nitrate respiratory anaerobically; glucose is fermented (usually with gas) via the mixed acid fermentation.

KEY BIOCHEMICAL REACTIONS

HABITAT

Part of the indigenous intestinal flora of warm-blooded animals; and in the case of E. blattae , of cockroaches.

PATHOGENICITY

Escherichia spp. is an opportunistic pathogen, but investigations have shown that a rather limited number of serovars or clones also play an important and more specific role in intestinal and extraintestinal diseases. Such clones often posses plasmids which provide them with special virulence traits.

The pathogenic E. coli strains have been divided into four groups according to their mechanism of virulence; Enteropathogenic, Enterotoxigenic, Enteroinvasive, and Enterohemorrhagic. (5) Enteropathogenic E. coli (EPEC) strains are a common cause of infant diarrhea in areas of poor sanitation. (5) The cause of travelers diarrhea are Enterotoxigenic E. coli (ETEC) strains, which produce enterotoxins that cause a gastroenteritis that is similar to a mild form cholera. (5) Enteroinvasive E. coli (EIEC) strains produce an invasive factor that produces a shigellosis-like dysentery in humans. (5) The Enterohemorrhagic E. coli (EHEC) group includes the infamous O157:H7 serogroup. Strains in the EHEC group produce enterotoxins (verotoxins) that cause severe bloody diarrhea (hemorrhagic colitis) and hemolytic uremic syndrome (HUS) in humans. (5)

E. coli is also a major cause of urinary tract infections and nosocomial infections including septicemia and meningitis. E. blattae has not been associated in disease of humans and or cockroaches.

RECOMMENDED MEDIA

For culture: Tryptic Soy Agar, Nutrient Agar, Blood Agar 5%.
For selective isolation: MacConkey Agar, EMB Agar, MacConkey with Sorbitol ( E. coli O157).
For maintenance: Tryptic Soy Agar, Nutrient Agar, Blood Agar 5%. For long-term storage at - 70 degrees C., TSB with 15% Glycerol or Skim Milk Media is recommended.

INCUBATION

Temperature: 35 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, MD4.

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.

5. Ray, Bibek. 1996. Fundamental Food Microbiology . CRC Press, Boca Raton, FL.


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