ESCHERICHIA COLI (E.coli)

ESCHERICHIA COLI (E.coli)

Escherichia coli (commonly abbreviated E. coli) is a Gram-negative, facultative anaerobic, rod shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls due to food contamination. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K, and by preventing the establishment of pathogenic bacteria within the intestine.

E. coli and related bacteria constitute gut flora, and fecal – oral transmission is the major route through which pathogenic strains of the bacterium cause disease. Cells are able to survive outside the body for a limited amount of time, which makes them ideal indicator organisms to test environmental samples for fecal contamination.

The bacterium can be grown easily and inexpensively in a laboratory setting, and has been intensively investigated for over 60 years. E. coli is the most widely studied prokaryotic model organism, and an important species in the fields of
 and microbiology, where it has served as the host organism for the majority of work with recombinant DNA.

MORPHOLOGY

E. coli is Gram-negative, facultative anaerobic and non-sporulating. Cells are typically rod-shaped, and are about 2.0 micrometers (μm) long and 0.25-1.0 μm in diameter, with a cell volume of 0.6–0.7 μm. It can live on a wide variety of substrates. Strains that possess flagella are motile. The flagella have a peritrichous arrangement.

CULTURAL CHARACTERISTICS

Escherichia coli or E.coli cells may grow on a solid or in a liquid growth medium under a laboratory condition. Solid and liquid media may have exactly the same composition except that the solid medium contains an extra 1.5% agar. Different E.coli clones may have different properties. Colonies growing on solid media represent different clones.

E.coli on EMB AGAR

E.coli on MACCONKEY AGAR

BIOCHEMICAL REACTIONS

E. coli uses mixed-acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol,  acetate and carbon dioxide. Since many pathways in mixedacid fermentation produce hydrogen gas, these pathways require the levels of hydrogen to be low, as is the case when E. coli lives together with hydrogenconsuming organisms, such as methanogens or sulphate-reducing bacteria.

CLICK FOR IMVIC AND TSI 
https://microbiologylaboratoryturkey.blogspot.com/2018/10/triple-sugar-iron-tsi-agar_4.html
https://microbiologylaboratoryturkey.blogspot.com/2018/09/imvic-test-test-methyl-red-test-voges.html
Gram Staining
https://microbiologylaboratoryturkey.blogspot.com/2018/09/gram-staining.html

LABORATORY DIAGNOSIS

E. coli infections can be diagnosed by the detection of E. coli in a laboratory test of your stool, urine, blood or other relevant sample. Infections with some types of E. coli, e.g. E. coli O157, can be detected by a serum antibody test.
Specimen used in lab for E.coli are

1. Urine
2. Stool

Culture
1. Isolation media- a) nutrient agar, b) MacConkey’s agar c) eosin- methylene
blue agar

Treatment of E coli infection

Patients, especially healthy adults, often require no treatment for E. coli O157:H7 since many infections are self–limited. Moreover, if required can be treated according to antibiotic sensitivity pattern.

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