Escherichia

(microbiology) A genus of bacteria in the family Enterobacteriaceae; straight rods occurring singly or in pairs.

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 also Diarrhea; Toxin.

A genus of widely distributed gram-negative bacteria in the family Enterobacteriaceae.

• E. coli — a species constituting the greater part of the normal intestinal flora of animals. The organism most used in recombinant DNA work. Pathogenic strains a cause of urinary tract infections, epidemic diarrheal diseases, especially in newborn animals and late respiratory disease in broiler chickens. Also a common opportunistic pathogen. See colibacillosis, coliform mastitis, coliform gastroenteritis, avian coliform septicemia, mastitis–metritis–agalactia, enteropathogenic, enterotoxigenic shiga-like toxins.
• E. coli 0157:H7 — a verotoxin producing E. coli that has been responsible for outbreaks of hemorrhagic colitis, especially in children, but in all ages. Case fatality rates can be high, especially where there is the complication of the hemolytic uremic syndrome (HUS). The organism is carried by cattle who show no sign of clinical disease and many outbreaks have been epidemiologically linked to food products of bovine origin. The mass handling and marketing of minced beef allow a contaminated batch to affect a large population. The infective dose for man is estimated at a few organisms and infection can also be picked up by children visiting petting zoos or on farm visits.
• E. coli J5 vaccine — vaccine prepared from E. coli mutant; provides protection against coliform mastitis in cows.
• attaching and effacing E. coli (AEEC) — produce shiga toxin (verotoxin). Certain serotypes cause enteritis, colitis and diarrhea in a number of different animal species by expressing a virulence factor protein called intimin which allows intimate attachment of the organism to the microvillus brush border of enterocyte forming a characteristic attaching and effacing lesion. Diagnosis is by the detection of the shiga toxin and characterisitic lesions.
• E. coli Shigella — a cluster of clones of E. coli that are unable to ferment lactose and that cause bacillary dysentery in primates, including humans, as a result of the independent acquisition of a specific virulence plasmid. Includes the organisms previously known as Shigella dysenteriae, S. flexneri, S. sonnei and S. boydii (now E. coli Dysenteriae, E. coli Flexneri, E. coli Sonnei and E. coli Boydii).

Escherichia
SEM micrograph of cluster of Escherichia coli bacteria. Each individual bacterium is oblong shaped
Scientific classification
Kingdom: Bacteria Phylum: Proteobacteria Class: Gammaproteobacteria Order: Enterobacteriales Family: Enterobacteriaceae Genus: Escherichia Castellani & Chalmers 1919
Species
E. albertii E. blattae E. coli E. fergusonii E. hermannii E. vulneris

Escherichia is a genus of Gram-negative, non-spore forming, facultatively anaerobic, rod-shaped bacteria from the family Enterobacteriaceae.^[1] Inhabitants of the gastrointestinal tracts of warm-blooded animals, Escherichia species provide a portion of the microbially-derived vitamin K for their host.

Pathogenesis

While many Escherichia are harmless commensals, particular strains of some species are human pathogens,^[2] and are known as the most common cause of urinary tract infections,^[3] significant sources of gastrointestinal disease, ranging from simple diarrhea to dysentery-like conditions,^[1] as well as a wide-range of other pathogenic states.^[4] While Escherichia coli is responsible for the vast majority of Escherichia-related pathogenesis, other members of the genus have also been implicated in human disease.^[5],[6]

See also

• E. coli O157:H7

References

1. ^ ^{a b} Madigan M; Martinko J (editors). (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1. 
2. ^ Guentzel MN (1996). Escherichia, Klebsiella, Enterobacter, Serratia, Citrobacter, and Proteus. In: Baron's Medical Microbiology (Baron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1. 
3. ^ Ronald A (2003). "The etiology of urinary tract infection: traditional and emerging pathogens". Dis Mon 49 (2): 71–82. doi:10.1016/S0011-5029(03)90001-0. PMID 12601338. 
4. ^ "The Species of Escherichia other than E. coli". The Prokaryotes. http://141.150.157.117:8080/prokPUB/chaphtm/142/11_00.htm. Retrieved 2006-05-05. 
5. ^ Pien FD, Shrum S, Swenson JM, Hill BC, Thornsberry C, Farmer JJ 3rd (1985). "Colonization of human wounds by Escherichia vulneris and Escherichia hermannii". J Clin Microbiol 22 (2): 283–5. PMID 3897270. 
6. ^ Chaudhury A, Nath G, Tikoo A, Sanyal SC (1999). "Enteropathogenicity and antimicrobial susceptibility of new Escherichia spp". J Diarrhoeal Dis Res 17 (2): 85–7. PMID 10897892. 

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