Escherichia coli
Escherichia coli is a bacterium, which inhabits the intestinal tract of humans and other warm-blooded mammals. It constitutes approximately 0.1% of the total bacteria in the adult intestinal tract. Its name comes from the name of the person, Escherich, who in 1885 first isolated and characterized the bacterium.
The bacterium, particularly one type called strain K–12, is one of the most widely studied organisms in modern research. Its biochemical behavior and structure are well known, having been studied for much of this century. This plethora of information has made E. coli indispensable as the bacterial model system for biochemical, behavioral and structural studies. E. coli is also the most encountered bacterium in clinical laboratories, being the primary cause of human urinary tract infections. Pathogenic (diseases causing) strains of E. coli are responsible for pneumonia, meningitis and traveler's diarrhea.
As part of the normal flora of the intestinal tract, E. coli is beneficial. It is crucial in the digestion of food, and is our principle source of vitamin K and B-complex vitamins. Outside of the intestinal tract, E. coli dies quickly. This trait has been exploited, and E. coli is a popular indicator of drinking water quality, as its presence indicates the recent contamination of the water with feces.
One of the most harmful types of E. coli is a strain called O157:H7. Researchers surmise that O157:H7 arose when an innocuous E. coli bacterium was infected by a virus carrying the genes coding for a powerful toxin called Shiga-like toxin. The toxin can destroy cells in the intestinal tract and, if they enter the bloodstream, can impair or destroy the kidneys and the liver. The intestinal damage causes a lot of bleeding. In children and elderly people, this hemorrhaging can be lethal. In other people, damage to the kidney and liver can be permanent or even lethal. In the summer of 2000, more than 2,000 people in Walkerton, Ontario, Canada were sickened and seven people died from drinking water which had been contaminated with O157:H7.
Strain O157:H7 was first linked to human disease in 1983, when it was shown to have been the cause of two outbreaks of an unusual and severe gastrointestinal ailment in the Unites States. Since then, the number of documented human illnesses and deaths caused by O157:H7 has increased steadily worldwide. Disease caused by E. coli is preventable, by proper hand washing after bowel movements, avoidance of unpasteurized milk or apple cider, washing of raw foods before consumption and thorough cooking of ground meat.
Modern genetics techniques have been successful in obtaining the sequence of the genetic material of E. coli. Frederick Blattner and his colleagues published the genome sequence of strain K–12 in 1997. The genome was discovered to have approximately 4300 protein coding regions making up about 88 per cent of the bacterial chromosome. The most numerous types of proteins were transport and binding proteins—those necessary for the intake of nutrients. A fairly large portion of the genome is reserved for metabolism—the processing of the acquired nutrients into useable chemicals. In 2000, Nicole Perna and her colleagues published the genome sequence of O157:H7. The O157:H7 genome shows similarity to tat of k12, reflecting a common ancestry. But, in contrast to K12, much of the genome of O157:H7 codes for unique proteins, over 1,300, some of which may be involved in disease causing traits. Many of these genes appear to have been acquired from other microorganisms, in a process called lateral transfer. Thus, strain O157:H7 appears to be designed to undergo rapid genetic change. This distinction is important; indicating that strategies to combat problems caused by one strain of E. coli might not be universally successful. Knowledge of the genetic organization of these strains will enable more selective strategies to be developed to combat E.coli infections.
Join eNotes
Over 3,500 study guides, question and answer forums, literature criticism, reference content, and much more!
