Escherichia coli O157:H7
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2008-07-12T22:06:45Z
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'''''Escherichia coli'' O157:H7''' is an [[enterohemorrhagic]] strain of the [[Bacteria|bacterium]] ''[[Escherichia coli]]'' and a cause of [[foodborne illness]].<ref name=Karch_2005>{{cite journal | author = Karch H, Tarr P, Bielaszewska M | title = Enterohaemorrhagic ''Escherichia coli'' in human medicine. | journal = Int J Med Microbiol | volume = 295 | issue = 6-7 | pages = 405–18 | year = 2005 | pmid = 16238016}}</ref> Based on a 1999 estimate, there are 73,000 cases of infection and about 60 deaths caused by ''E.coli'' O157:H7 each year in the [[United States]].{{Fact|ref talk about E. coli in general, not only about E.coli O157:H7|date=March 2008}}<ref name=CDC>[http://www.cdc.gov/ecoli/qa_ecoli_sickness.htm Questions & Answers: Sickness caused by E. coli], Centers for Disease Control and Prevention.</ref> Infection often leads to bloody [[diarrhea]], and occasionally to [[kidney]] failure, especially in young [[children]] and elderly people. Most illness has been associated with eating undercooked, contaminated ground [[beef]], drinking [[unpasteurized]] [[milk]], swimming in or drinking contaminated water, and eating contaminated vegetables.
== Bacteriology ==
''E. coli'' serotype... O157:H7 is a [[gram-negative]] rod-shaped bacterium. The letter "O" in the name refers to the [[somatic antigen]] number, whereas the "H" refers to the [[flagellum|flagella]] antigen. Other serotypes may cause (usually less severe) illness, but only those with the specific O157:H7 combination are reviewed here. Other bacteria may be classified by "K" or capsular antigens. (The "O" stands for ''ohne Hauch'' [Ger. "without breath" or "without film"]; "H" for ''Hauch''; and "K" for ''Kapsel''.<ref>See [[:de:Kauffmann-White-Schema|Kauffmann-White-Schema]] in the German Wikipedia.</ref><ref>[http://www.mercksource.com/pp/us/cns/cns_hl_dorlands_split.jsp?pg=/ppdocs/us/common/dorlands/dorland/nine/000950436.htm O antigen] at Dorlands Medical Dictionary.</ref>) This is one of hundreds of serotypes of the [[bacterium]] ''[[Escherichia coli]]''. While most strains are harmless and normally found in the intestines of mammals, this strain may produce [[Shiga-like toxin]]s, cause severe illness, and is a member of a class of pathogenic ''E. coli'' known as enterohemorrhagic ''Escherichia coli'' or EHEC. Sometimes also referred to by their toxin producing capabilities, Verocytotoxin producing ''E. coli'' (VTEC) or Shiga-like Toxin producing ''E. coli'' (STEC).
''E. coli'' O157:H7 was first recognized as a pathogen as a result of an outbreak of unusual gastrointestinal illness in [[1982]]. The outbreak was traced to contaminated [[hamburger]]s, and the illness was similar to other incidents in the United States and Japan. The etiologic agent of the illness was identified as a rare O157:H7 serotype of ''Escherichia coli'' in 1983. This serotype had only been isolated once before, from a sick patient in 1975.<ref name=Riley_1983>{{cite journal | author = Riley L, Remis R, Helgerson S, McGee H, Wells J, Davis B, Hebert R, Olcott E, Johnson L, Hargrett N, Blake P, Cohen M | title = Hemorrhagic colitis associated with a rare ''Escherichia coli'' serotype. | journal = N Engl J Med | volume = 308 | issue = 12 | pages = 681–5 | year = 1983 | pmid = 6338386}}</ref>
''E. coli'' O157:H7 is markedly different from other pathogenic E. coli, as well. In particular, the O157:H7 serotype is negative for invasiveness ([[sereny test]]), elaborates no [[colonization factor]]s ([[CFA/I]] or [[CFA/II]]), doesn't produce heat stable or heat [[labile toxins]] and is [[non-hemolytic]]. In addition, ''E. coli'' O157:H7 is usually [[sorbitol]] negative whereas 93% of all E. coli ferment sorbitol.<ref name=wells_1983_101>Wells, J. G., B. R. Davis, I. K. Wachsmuth, L. W. Riley, R. S. Remis, R. Sokolow, and G. K. Morris. 1983. Laboratory investigation of hemorrhagic colitis outbreaks associated with a rare Escherichia coli serotype. J. Clin. Microbiol. 18:512-520.</ref> ''E. coli'' O157:H7 also lacks the ability to hydrolyze [[4-methylumbelliferyl-β-D-glucuronide]] (MUG)<ref name=Doyl_1984_24/> and does not grow at 45 °C in the presence of 0.15% [[bile salts]]. Because of the latter characteristic this serotype cannot be isolated by using standard fecal coliform methods that include incubation at 45 °C.<ref name=Doyl_1984_24>Doyle, M. P., and J. L. Schoeni. 1984. Survival and growth characteristics of Escherichia coli associated with hemorrhagic colitis. Appl. Environ. Microbiol. 48:855-856.</ref><ref name=Szabo_1986_92>Szabo, R. A., E. C. D. Todd, and A. Jean. 1986. Method to isolate Escherichia coli O157:H7 from food. J. Food Prot. 49:768-772.</ref>
''E. coli'' O157:H7 serotypes are closely related, descended from a common ancestor, divergent in plasmid content more than chromosomal content, and are no more related to other [[shiga toxin]] producing strains than any other randomly chosen E. coli serotype. ''E. coli'' O55:H7 and ''E. coli'' O157:H7 are most closely related and diverged from a common pathogenic ancestor that possessed the ability to form attaching and effacing lesions. ''E. coli'' O157:H7 serotypes apparently arose as a result of [[horizontal gene transfer]] of virulence factors.<ref name=Whittam_1988_102>Whittam, T. S., I. K. Wachsmuth, and R. A. Wilson. 1988. Genetic evidence of clonal descent of Escherichia coli O157:H7 associated with hemorrhagic colitis and hemolytic uremic syndrome. The Journal of Infectious Diseases 157:1124-33.</ref>
Among these virulence factors are a periplasmic catalase and [[Shiga toxin|shiga-like toxins]]. Shiga-like toxins are iron regulated toxins that catalytically inactivate [[60S]] ribosomal subunits of eukaryotic cells blocking [[mRNA]] translation and causing cell death.<ref name=reisberg_1981_72>Reisberg, R., S. Olsnes, and K. Eiklid. 1981. The cytotoxic activity of shigella toxin. J. Biol. Chem. 256:8739-8744.</ref>
Shiga-like toxins are functionally identical to toxins produced by virulent Shigella species.<ref name=Calderwood_1987_12>Calderwood, S. B., F. Auclair, A. Donohue-Rolfe, G. T. Keusch, and J. J. Mekalanos. 1987. Nucleotide sequence of the shiga-like toxin genes of Escherichia coli. Proc. Natl. Acad. Sci. USA 84:4364-4368.</ref>
Strains of ''E. coli'' that express shiga-like toxins gained this ability due to [[Transduction (genetics)|infection with a prophage]] containing the structural coding for the toxin, and non-producing strains may become infected and produce shiga-like toxins after incubation with shiga toxin positive strains.<ref nameO'Brien_1984_65=>O'Brien, A. D., J. W. Newland, S. F. Miller, and R. K. Holmes. 1984. Shiga-like toxin-converting phages from Escherichia coli strains that cause hemorrhagic colitis or infantile diarrhea. Science 226:694-696.</ref><ref name=Strockbine_1986_91>Strockbine, N. A., L. R. M. Marques, J. W. Newland, H. W. Smith, R. K. Holmes, and A. D. O'Brien. 1986. Two toxin-converting phages from Escherichia coli O157:H7 strain 933 encode antigenically distinct toxins with similar biologic activities. Infect. Immun. 53:135-140.</ref>
The periplasmic catalase is encoded on the [[pO157]] plasmid and is believed to be involved in virulence by providing additional oxidative protection when infecting the host.<ref name=Brunder_1996_11>Brunder, W., H. Schmidt, and H. Karch. 1996. KatP, a novel catalase-peroxidase encoded by the large plasmid of enterohaemorrhagic Escherichia coli O157:H7. Microbiology 142:3305-3315.</ref>
== Transmission ==
A major source of infection is undercooked ground beef; other sources include consumption of unpasteurized milk and juice, raw [[sprouts]], [[lettuce]], and [[salami]], and contact with infected live animals. Disease caused by ''E.coli'' O157:H7 is known as the "hamburger disease" because of its association with eating home-made [[hamburgers]]. Association with hamburgers from commercial [[fast food]] chains has become rare as the chains now use cooking procedures designed to destroy the bacteria.
Waterborne transmission occurs through swimming in contaminated lakes, pools, or drinking inadequately treated water. The organism is easily transmitted from person to person and has been difficult to control in child day-care centers.
''E.coli'' O157:H7 is found on cattle farms and can live in the intestines of healthy cattle. The toxin requires highly specific [[Receptor (biochemistry)|receptor]]s on the cells' surface in order to attach and enter the cell; species such as [[cattle]], [[swine]], and [[deer]] which do not carry these receptors may harbor toxigenic bacteria without any ill effect, shedding them in their feces from where they may be spread to humans. Meat can become contaminated during slaughter, and organisms can be thoroughly mixed into beef when it is ground into hamburger. Bacteria present on the cow's [[udder]]s or on equipment may get into raw milk. Although the number of organisms required to cause disease is not known, it is suspected to be very small.
Eating contaminated meat (especially ground meat) or produce that has not been cooked sufficiently to kill ''E. coli'' O157:H7 can cause infection. Contaminated foods look, smell and taste normal.
== Signs and symptoms ==
''E. coli'' O157:H7 infection often causes severe, acute bloody diarrhea (although non-bloody diarrhea is also possible) and abdominal [[cramp]]s. Usually little or no [[pyrexia|fever]] is present, and the illness resolves in 5 to 10 days. It can also be [[asymptomatic]].
In some people, particularly children under 5 years of age and the elderly, the infection can cause [[haemolytic uremic syndrome]], in which the [[red blood cell]]s are destroyed and the kidneys fail. About 2%–7% of infections lead to this complication. In the United States, haemolytic uremic syndrome is the principal cause of [[acute kidney failure]] in children, and most cases of haemolytic uremic syndrome are caused by ''E. coli'' O157:H7.
== Diagnosis ==
A [[Stool test|stool culture]] can detect the bacterium, although it is not a routine test and so must be specifically requested. The sample is cultured on [[sorbitol-MacConkey agar|sorbitol-MacConkey]] (SMAC) [[agar]], or the variant cefeximine potassium tellurite sorbitol-MacConkey agar (CT-SMAC). However, like all cultures, diagnosis is slow using this method, and more rapid diagnosis is possible using [[polymerase chain reaction|PCR]] techniques. Newer technologies using [[fluorescent]] and [[antibody]] detection are also under development.
===Surveillance===
''E. coli'' O157:H7 infection is nationally reportable in the USA and Great Britain, and is reportable in most U.S. states. HUS ([[hemolytic-uremic syndrome]]) is also reportable in most US states.
== Treatment ==
Most people recover without [[antibiotic]]s or other specific treatment in 5–10 days. There is no evidence that antibiotics improve the course of disease, and it is thought that treatment with some antibiotics may precipitate kidney complications.<ref>{{cite journal
| last = Walterspiel
| first = J. N.
| coauthors = Morrow, Ardythe L.; Cleary, T. G.; Ashkenazi, S
| title = Effect of subinhibitory concentrations of antibiotics on extracellular shiga-like toxin I
| journal = Infection
| volume = 20
| pages = 25–29
| date = 2003
| url = http://www.springerlink.com/content/gn87605160632v3k/
| id =
| accessdate = 200-01-07
| doi = 10.1007/BF01704889 }}</ref> Antidiarrheal agents, such as [[loperamide]] (imodium), should also be avoided.
[[Hemolytic-uremic syndrome]] is a life-threatening condition usually treated in an [[intensive care unit]]. [[Blood transfusion]]s and [[kidney dialysis]] are often required. With intensive care, the death rate for hemolytic uremic syndrome is 3%–5%.
== Prognosis ==
The majority of infections resolve completely. Those who develop hemolytic uremic syndrome suffer more long-term consequences. 3–5% of those with HUS die, causing about 61 deaths annually in the USA. One third of this group have abnormal kidney function many years later, and a few require long-term [[dialysis]]. Another 8% of this group develop other lifelong complications, such as high [[blood pressure]], [[seizure]]s, [[blindness]], [[paralysis]], and, if surgery is required to remove part of the bowel, additional procedure-related side-effects.
There are currently long term studies continuing in [[Walkerton, Ontario]], looking at the long term effects of ''E. coli'' O157:H7 after approximately 2500 people were infected through the municipal water system in May 2000.
=== Costs ===
The pathogen results in an estimated 2,100 hospitalizations annually in the United States. The illness is often misdiagnosed; therefore, expensive and invasive diagnostic procedures may be performed. Patients who develop HUS often require prolonged hospitalization, dialysis, and long-term follow-up.
== Prevention ==
===Agricultural===
Beef processing is a common point of contamination, if during the slaughtering process the contents of intestines or fecal material on the hide mix with the meat and bacteria flourish in the warm, moist conditions. If the infected parts are then ground, the bacteria goes from the surface of the cut to the interior of the ground mass. Thus, ground beef is much more likely to be a source of infection than steak. In steak only the surface area of a cut is exposed during butchering, and cooking the outside affects the entire exposed portion. In ground beef, however, bacteria is mixed throughout the meat mass, requiring the entire mass to be heated thoroughly to eliminate the pathogen. Additionally, in the production of ground beef, meat from multiple cows is often ground together, enabling contamination from a single cow to infect an entire lot of ground beef.
Accordingly, reduction of infection requires preventive measures that either reduce the number of cattle that carry ''E.coli'' O157:H7 or reduce the contamination of meat during slaughter and grinding.
In [[January 2007]] Canadian bio-pharmaceutical company [[Bioniche]] announced it had developed a bovine vaccine capable of reducing O157:H7 in cattle by over 99%.<ref>{{cite web | title = Canadian Research Collaboration Produces World's First Food Safety Vaccine: Against E. coli 0157:H7 | work = CNX Marketlink | url = http://www.cnxmarketlink.com/en/releases/archive/January2007/10/c4698.html | accessdate = 2007-09-15 }}</ref>
===Culinary and dietary===
Cooking all ground beef and hamburgers thoroughly, and checking the temperature using an instant-red meat [[thermometer]], will eliminate the organism. Ground beef should be cooked until a thermometer inserted into several parts of the patty, including the thickest part, reads at least 72 °C (160 °F).
When preparing meat, it should be kept separate from other food items and all surfaces and utensils which come into contact with raw meat should be washed thoroughly before being used again. [[Hand washing]] is similarly important. Placing cooked hamburgers or ground beef on an unwashed plate that held raw patties can transmit infection.
Avoid unpasteurized milk, juice, and [[cider]]. Commercial juice is almost always pasteurized, and juice concentrates are also heated sufficiently to kill [[pathogen]]s.
Fruits and vegetables should be washed thoroughly, especially those that will not be cooked. Children under 5 years of age, immune-compromised persons, and the elderly should avoid eating [[alfalfa]] sprouts until their safety can be assured. Methods to decontaminate alfalfa [[seed]]s and [[sprout]]s are being investigated.
Contaminated water should be boiled at a rolling boil for at least one minute (longer at higher altitudes) before consumption. Care while swimming to avoid ingestion of potentially contaminated water can reduce the chances of infection.
Proper [[hand washing]] after using the lavatory or changing a diaper, especially among children or those with diarrhea, will reduce the risk of transmission. Anyone with a diarrheal illness should avoid swimming in public pools or lakes, sharing baths with others, and preparing food for others.
===Opportunities===
Learning more about the ecology of this organism in cattle and other ruminants may help in devising methods to decrease its prevalence in food animals. Learning how this pathogen contaminates produce items could lead to measures that would increase their safety. Decreasing the incidence of these infections would decrease HUS, the major cause of kidney failure in children in the United States. Transmission in [[day care]] centers highlights need for better infection-control practices.
(''adapted from two public domain sources''[http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm], [http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_t.htm])
==Trivia==
The now defunct band I Mother Earth recorded a song titled 0157:H7 on their album The Quicksilver Meat Dream.
==See also==
*[[List of foodborne illness outbreaks]]
*[[Centers for Disease Control and Prevention|CDC]]
==External links==
* For more information about reducing your risk of foodborne illness, visit the US Department of Agriculture's Food Safety and Inspection Service website at: http://www.fsis.usda.gov or the Partnership for Food Safety Education at:
* For more advice on cooking ground beef, visit the U.S. Department of Agriculture web site at: http://www.fsis.usda.gov/OA/topics/gb.htm
* [http://briandeer.com/e-coli-o157.htm briandeer.com] - report from [[The Sunday Times]] on a UK outbreak, May 17 1998
* [http://cbs5.com/topstories/local_story_257194412.html CBS5 report on september 2006 outbreak]
* Genome information is available from the [http://www.ericbrc.org NIAID Enteropathogen Resource Integration Center (ERIC)]
==References==
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