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Escherichia Coli: Strains
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Escherichia coli is a common member of the normal flora of the large intestine. As long as these bacteria do not acquire genetic elements encoding for virulence factors, they remain benign commensals. Strains that acquire bacteriophage or plasmid DNA encoding enterotoxins or invasion factors become virulent and can cause either a plain, watery diarrhea or an inflammatory dysentery. These diseases are most familiar to Westerners as traveler's diarrhea, but they are ... major health problems in endemic countries, particularly among infants. Three groups of E coli are associated with diarrheal diseases. Escherichia coli strains that produce enterotoxins are called enterotoxigenic E coli (ETEC).
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Escherichia coli strain K-12 is arguably the single organism about which the most is known. Originally isolated in 1922, it was catapulted to prominence by the discovery of strain K-12's ability to carry out genetic recombination by conjugation (1) and, soon after, by generalized transduction (2). The strain K-12 has been widely distributed to laboratories across the world. Over the ensuing years it became the primary model organism for basic biology, molecular genetics and physiology of bacteria, and was the founding workhorse of the biotechnology industry.
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Escherichia coli strains isolated from extraintestinal infections often possess a number of properties not usually found in random fecal isolates. These include production of soluble and cell-bound hemolysins, the colicin V plasmid, production of the siderophores aerobactin and enterochelin, and special pilial antigens for adherence to target cells. The hemolysin kills host cells and makes iron more available by releasing hemoglobin-bound iron from lysed red cells. To strip iron from the host iron-binding proteins ( transferrin and lactoferrin), E coli produces siderophores of both the hydroxamate (aerobactin) and phenolate (enterochelin) types. Common or type 1 pili may mediate adherence to bladder cells; P-pili are virulence factors for strains causing pyelonephritis; S-pili, which recognize O-linked sialo-oligosaccharides of glycophorin A, are associated with meningitis and urinary tract infections. Certain afimbrial adhesions and outer membrane proteins ... have been associated with urinary tract infections.
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Escherichia coli is used extensively in genetic research. New strains are created and subjected to doses of radiation, making them unable to survive in the "wild". This protects against the possibility of a strain escaping from a laboratory.
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Most strains of Escherichia coli form part of the normal intestinal microflora in humans and warm-blooded animals. However, some strains have the ability to cause disease in humans through the presence of specific virulence factors.
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A bacillus (Escherichia coli) normally found in the human gastrointestinal tract and existing as numerous strains, some of which are responsible for diarrheal diseases. Other strains have been used experimentally in molecular biology.
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