Escherichia(redirected from Escherichia coli Shigella)
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A genus of bacteria named for Theodor Escherich, an Austrian pediatrician and bacteriologist, who first published on these bacteria in 1885. Escherichia coli is the most important of the six species which presently make up this genus, and it is among the most extensively scientifically characterized living organisms. Escherichia coli are gram-negative rod-shaped bacteria approximately 0.5 × 1–3 micrometers in size. Molecular taxonomic analysis based on the nucleotide sequences of ribosomal ribonucleic acid (RNA) has revealed that Shigella, a bacterial genus of medical importance previously thought to be distinct from E. coli, is actually the same species.
The natural habitat of E. coli is the colon of mammals, reptiles, and birds. In humans, E. coli is the predominant bacterial species inhabiting the colon that is capable of growing in the presence of oxygen. The presence of E. coli in the environment is taken to be an indication of fecal contamination.
Most strains of E. coli are harmless to the humans and other animals they colonize, but some strains can cause disease when given access to extraintestinal sites or the intestines of noncommensal hosts. Escherichia coli is the most important cause of urinary tract infections. Women are more susceptible than men; four out of ten women experience at least one urinary tract infection in their lifetime. Urinary tract infections may extend into the bloodstream, especially in hospitalized patients whose defenses are compromised by the underlying illness. This may lead to a type of whole-body inflammatory response known as sepsis, which is frequently fatal. Certain E. coli strains can invade the intestine of the newborn and cause sepsis and meningitis. These strains are acquired at birth from E. coli which have colonized the vagina of the mother.
Several different strains of E. coli cause intestinal infections. In the developing world, the most important of these are the enterotoxigenic E. coli, which produce enterotoxins that act on the epithelial cells lining the small intestine, causing the small intestine to reverse its normal absorptive function and secrete fluid. This leads to a dehydrating diarrhea which can be fatal, especially in poorly nourished infants. Therapy consists of oral or, in serious cases, intravenous rehydration. Enterotoxigenic E. coli are transmitted by ingestion of fecally contaminated water and food, and are a common cause of diarrheal disease in travelers in developing countries.
An important group of pathogenic E. coli in developed countries are the enterohemorrhagic strains, especially the serotype known as E. coli O157:H7. These strains are normal in cattle but cause bloody diarrhea in humans. A complication of approximately 10% of cases is a potentially fatal disease known as hemolytic uremic syndrome. The virulence of these strains involves the close attachment of bacteria to epithelial cells lining the colon, resulting in alteration of the epithelial cell structure, and the production of Shiga toxin. The toxin enters the bloodstream after being absorbed in the colon and damages the endothelial cells lining the blood vessels of the colon, resulting in bloody diarrhea. In cases of hemolytic uremic syndrome, the toxin circulating in the blood damages blood vessels in the kidney, resulting in kidney failure and anemia. Enterohemorrhagic E. coli are acquired by the ingestion of undercooked beef, uncooked vegetables, or unpasteurized juices from fruits which have been contaminated with the feces of infected cattle. An infection can also be acquired from contact with a human infected with the organism and from contaminated water. Children and the elderly are at greatest risk of developing hemolytic uremic syndrome.
Other strains which are pathogenic in the human colon include the enteroinvasive E. coli (including Shigella) and the enteropathogenic E. coli. Enteroinvasive E. coli cause a disease called bacillary dysentery characterized by bloody diarrhea. Enteropathogenic E. coli have been associated with protracted diarrhea in infants and can occasionally cause severe wasting. See Toxin
a genus of bacteria of the family Enterobacteriaceae; the type species is E. coli (seeCOLON BACILLUS). The bacteria are not usually pathogenic, but they can cause disease in the kidneys, urinary bladder, and gallbladder.