1. IDENTIFYING CHARACTERISTICS
2. TAXONOMIC DESCRIPTION
Members of this genus are almost universal inhabitants of the intestinal tract of humans and warm-blooded animals. Escherichia play an important nutritional role in the synthesizing of vitamins, specially vitamin K. Wild-type strains show no growth-factor requirements and can grow on many different energy and carbon sources. As enterics they can ferment glucose (and many other carbohydrates), and transform them into all of the macromolecular components that make up the cell. Colonization and attachment of the small intestine is accomplished through the production of K antigen. Motility is achieved by means of peritrichous flagella that it can use to respond to changes in pH, temperature, and osmolarity to name a few.
There are over 700 serotypes of E. coli alone, of which some are pathogenic. All of these different antigenic types can be characterized by means of their O, H, and K antigens. Of all pathogenic strains O157:H7 has become the best known. This particular E. coli strain is an enterohaemorrhagic pathogen, is responsible for hundreds of deaths each year, worldwide, and is spread primarily through contaminated meat and poultry products.
3. ISOLATION AND ECOLOGY
Escherichia can be cultured on different highly selective media, and upon isolation will look off-white, dark blue, cream, or metallic green. Escherichia are easily isolated on Eosin Methylene Blue Agar on which they demonstrate a greenish metallic sheen. The table below demonstrates some of the biochemical characteristics of E. coli
Escherichia belong to a large bacterial family known as the Enterobacteriaceae, or enteric bacteria. All enteric bacteria are facultatively anaerobic Gram-negative rods that live in the GI tract of animals. Of all Escherichia species, E. coli are by far the best known and studied as its entire genome has been sequenced. E. coli are is the predominant facultative organism in the human GI tract. They are very important organisms from a medical stand point as they provide us with a source of vitamins K and B. Though E. coli can be considered benign, there are a few strains which cause disease in humans. One such rare strain is E. coli O157:H7, a member of the enterohemorrhagic E. coli group. These bacteria can cause hemorrhaging which can eventually lead to death. E. coli has been used as an indicator of fecal pollution in water (as a fecal coliform) for over 100 years.
H2S |
Urease |
VP |
Indole |
Motility |
Gas from glucose |
ß-Galactosidase |
- |
- |
- |
+ |
- or + |
+ |
+ |
KCN |
Citrate |
Mucate Utilization |
Phenyl-Methyl Red |
Tartrate Utilization |
Alanine Deaminase |
DNA %GC |
- |
- |
+ |
+ |
+ |
- |
48-52 |
4. ADDITIONAL SOURCES OF INFORMATION
Holt, J.G., N.R. Krieg, P.H.A. Sneath, J.T. Staley, and S.T.
Williams. 1994. Bergey's Manual of Systematic Bacteriology.
Williams and Wilkins. Baltimore, Maryland. Section 5, pp. 408-506.
Madigan, M.T., J.M. Martinko, and J. Parker. 2000. Brock Biology of Microorganisms. Prentice-Hall, Inc. Upper Saddle River, New Jersey. pp.480.
5. LINKS TO OTHER SITES ON ESCHERICHIA
| HOME PAGE | SYLLABUS | CHAPTERS | PROJECT | LINKS |
| MICROBES | SOILS | CYCLES | APPLICATIONS |