Monday, 8 March 2021

ESCHERICHIA COLI - An Overview

ESCHERICHIA COLI

Domain: Bacteria
Phylum: Proteobacteria
Class:     Gammaproteobacteria
Order:    Enterobacteriales
Family:  Enterobacteriaceae
Genus:   Escherichia
Species: E.Coli

Escherichia Coli originally called "Bacterium colicommune," was first isolated from the feces of a child in 1885 by the Austrian paediatrician Theodor Escherich.

Habitat

- Escherichia coli is a common inhabitant of the gastrointestinal tract of humans and animals.
- Escherichia coli can be found secondarily in soil and water as the result of fecal contamination.

Morphology

- Escherichia coli are Gram-negative, nonperforming bacilli.
- They are approximately 0.5 μm in diameter and 1.0-3.0 μm in length.
- Escherichia coli are commonly motile in liquid by means of peritrichous flagella.
- Escherichia coli are commonly fimbriated.
- In addition, a slime layer, colonic acid extracellular polysaccharide, common to many E.coli isolates.

Physiology

- Escherichia coli is a facultative anaerobe.
- Most E.coli strains are capable of growing over a wide temperature (approximately 15-48°C).
- The growth rate is maximal in the narrow range of 37- 42 °C.
- Escherichia coli can grow within a pH range of approsimately 5.5-8.0 with best growth occurring at neutrality.
- Some diarrheagenic E.coli strains haye the ability to tolerate exposure to pH 2.0.
- Such an acid shock mimics fransit through the stomach and induces expression of sets of genes involved in survival and pathogenesis.

Growth & Nutrition

- It is capable of reducing nitrates to nitrites.
- When growing fermentatively on glucose or other carbohydrates, it produces acid and gas.
- E.coli is positive for indole production and the methyl red test.
- Most strains are oxidase, citrate, urease and hydrogen sulfide negative.
- The classic differential test to primarily separate E.coli from Shigella and Salmonella is the ability of E.coli to ferment lactose, which the latter two genera fail to do.
- Aside from lactose, most E.coli strains can also ferment D-mannitol, D- sorbitol, and Larabinose, maltose, D-xylose, trehalose and D-mannose. There are limited instances where pathogenic strains differ from the commensals in their metabolic abilities.
- For example, commensal E.coli strains generally use sorbitol, but E.coli O157:H7 does not. Most diarrheagenic strains cannot utilize D-serine as a carbon and nitrogen source, but uropathogenic and commensal fecal strains can use this enantiomer of serine

Genetics

- The mol% G + C of the DNA is 39-65 %.

Economic importance &/or Pathogenesis

- Enteropathogenic E.coli is a significant cause of infant diarrhea in developing nations.
- E.coli (EPEC) was historically recognized on the basis of serotypes su as O55:H6 and O127:H6. They are currently defined as those diarrheagenic E.coli strains.
- Enterohemorrhagic E.coli the ability to cause a disease of the large intestine that may present as simple watery diarrhea and then progress to bloody stools with ulcerations of the bowel.
- Enteroaggregative E.coli (EAEC) disease, as described by human volunteers, is a watery diarrhea that occurs in some cases with abdominal cramps, but no fever
- Extraintestinal E.coli Two separate pathotypes of E.coli are generally recognized causes of extraintestinal human diseases (neonatal septicemia)
- Meningitis E.coli [meningitis-associated E.coli, MAEC] and the urinary tract and bloodstream E.coli [uropathogenic E.coli, UPEC].
- Some isolates, E.coli O18:K1:H7, are recognised as having the potential to cause both invasive neonatal diseases and urinary tract infections.

Examples

Escherichia vulneris
Escherichia albertii
Escherichia fergusonii  

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