Escherichia coli O157:H7: Difference between revisions

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''[[Escherichia coli|E. coli]]'' O157:H7 is markedly different from other [[Pathogen|pathogenic]] [[Escherichia coli|E. coli]], as well. In particular, the O157:H7 serotype is negative for invasiveness (sereny test), elaborates no colonization factors (CFA/I or CFA/II), doesn't produce heat stable or heat labile toxins, and is non-hemolytic. In addition, ''[[Escherichia coli|E. coli]]'' O157:H7 is [[sorbitol]] negative whereas 93% of all [[Escherichia coli|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>  ''[[Escherichia coli|E. coli]]'' O157:H7 also lacks the ability to hydrolyze 4-methylumbelliferyl-ß-D-glucuronide (MUG) 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 [[Feces|fecal]] [[Coliform bacteria|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>
''[[Escherichia coli|E. coli]]'' O157:H7 is markedly different from other [[Pathogen|pathogenic]] [[Escherichia coli|E. coli]], as well. In particular, the O157:H7 serotype is negative for invasiveness (sereny test), elaborates no colonization factors (CFA/I or CFA/II), doesn't produce heat stable or heat labile toxins, and is non-hemolytic. In addition, ''[[Escherichia coli|E. coli]]'' O157:H7 is [[sorbitol]] negative whereas 93% of all [[Escherichia coli|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>  ''[[Escherichia coli|E. coli]]'' O157:H7 also lacks the ability to hydrolyze 4-methylumbelliferyl-ß-D-glucuronide (MUG) 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 [[Feces|fecal]] [[Coliform bacteria|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>
''E. coli'' O157:H7 [[Serotype|serotypes]] are closely related, descended from a common ancestor, divergent in [[plasmid]] content more than [[Chromosome|chromosomal]] content, and are no more related to other [[shiga toxin]] producing [[Strain (biology)|strains]] than any other randomly chosen [[Escherichia coli|E. coli]] [[serotype]]. ''[[Escherichia coli|E. coli]]'' O55:H7 and ''[[Escherichia coli|E. coli]]'' O157:H7 are the most closely related and diverged from a common [[Pathogen|pathogenic]] ancestor that possessed the ability to form attaching and effacing lesions. ''[[Escherichia coli|E. coli]]'' O157:H7 [[Serotype|serotypes]] apparently arose as a result of [[horizontal gene transfer]] of [[Virulence factor|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>
Among these [[Virulence factor|virulence factors]] are a periplasmic [[catalase]] and [[Shiga toxin|shiga-like toxins]]. [[Shiga-like toxin|Shiga-like toxins]] are [[iron]] regulated [[Toxin|toxins]] that [[Catalysis|catalytically]] inactivate [[60S]] [[Ribosome|ribosomal]] subunits of [[Eukaryote|eukaryotic cells]] blocking [[Messenger RNA|mRNA]] [[Translation (biology)|translation]] and causing [[Cell (biology)|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 toxin|Shiga-like toxins]] are functionally identical to [[Toxin|toxins]] produced by [[Virulence|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> [[Strain (biology)|Strains]] of ''[[Escherichia coli|E. coli]]'' that express [[Shiga-like toxin|Shiga-like toxins]] gained this ability due to [[Transduction (genetics)|infection with a prophage]] containing the structural [[coding]] for the [[toxin]], and non-producing [[Strain (biology)|strains]] may become [[Infection|infected]] and produce [[Shiga-like toxin|Shiga-like toxins]] after incubation with [[Shiga toxin]] positive [[Strain (biology)|strains]].<ref>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 [[Encoding (memory)|encoded]] on the pO157 [[plasmid]] and is believed to be involved in [[virulence]] by providing additional [[Redox|oxidative]] protection when [[Infection|infecting]] the [[Host (biology)|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>
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>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 ==
== Transmission ==
The major source of [[infection]] is under cooked ground [[beef]]; other sources include consumption of [[Raw milk|unpasteurized milk]] and juice, raw sprouts, [[lettuce]], and salami, and contact with [[infected]] live animals. Waterborne [[Transmission (medicine)|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.
The major source of [[infection]] is under cooked ground [[beef]]; other sources include consumption of [[Raw milk|unpasteurized milk]] and juice, raw sprouts, [[lettuce]], and salami, and contact with [[infected]] live animals. Waterborne [[Transmission (medicine)|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 a small number of cattle farms and can live in the [[intestine]] of healthy cattle. The [[toxin]] requires highly specific [[Receptor (biochemistry)|receptor]]s on the [[Cell (biology)|cells']] surface in order to attach and enter the [[Cell (biology)|cell]]; [[species]] such as cattle, swine, and deer that do not carry these [[Receptor (biochemistry)|receptors]], may harbor [[Toxin|toxigenic]] [[bacteria]] without any ill effect, shedding them in their feces from where they may spread to humans. Meat can become contaminated during harvest, and [[Organism|organisms]] can be thoroughly mixed into [[beef]] when it is ground. [[Bacteria]] present on the cow's udders or on equipment may get into [[raw milk]]. Although the number of [[Organism|organisms]] required to cause [[disease]] is not known, it is suspected to be very small.
''[[Escherichia coli|E.coli]]'' O157:H7 is found on a small number of cattle farms and can live in the [[intestine]] of healthy cattle. The [[toxin]] requires highly specific [[Receptor (biochemistry)|receptor]]s on the [[Cell (biology)|cells']] surface in order to attach and enter the [[Cell (biology)|cell]]; [[species]] such as cattle, swine, and deer that do not carry these [[Receptor (biochemistry)|receptors]], may harbor [[Toxin|toxigenic]] [[bacteria]] without any ill effect, shedding them in their feces from where they may spread to humans. Meat can become contaminated during harvest, and [[Organism|organisms]] can be thoroughly mixed into [[beef]] when it is ground. [[Bacteria]] present on the cow's udders or on equipment may get into [[raw milk]]. Although the number of [[Organism|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 and smell normal.
Eating contaminated meat (especially ground meat) or produce that has not been cooked sufficiently to kill ''[[Escherichia coli|E. coli]]'' O157:H7, can cause infection. Contaminated foods look and smell normal.


== Signs and Symptoms ==
== Signs and Symptoms ==
''E. coli'' O157:H7 [[infection]] often causes severe, acute [[Blood|bloody]] [[diarrhea]] (although non [[Blood|bloody]] [[diarrhea]] is also possible) and [[Abdomen|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]].
''[[Escherichia coli|E. coli]]'' O157:H7 [[infection]] often causes severe, acute [[Blood|bloody]] [[diarrhea]] (although non [[Blood|bloody]] [[diarrhea]] is also possible) and [[Abdomen|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 [[hemolytic uremic syndrome]], in which the [[red blood cell]]s are destroyed and the [[Kidney|kidneys]] fail. About 2%-7% of [[Infection|infections]] lead to this [[Complication (medicine)|complication]]. In the United States, [[Hemolytic-uremic syndrome|hemolytic uremic syndrome]] is the principal cause of [[acute kidney failure]] in children, and most cases of [[Hemolytic-uremic syndrome|hemolytic uremic syndrome]] are caused by ''E. coli'' O157:H7.
In some people, particularly children under 5 years of age and the elderly, the [[infection]] can cause [[hemolytic uremic syndrome]], in which the [[red blood cell]]s are destroyed and the [[Kidney|kidneys]] fail. About 2%-7% of [[Infection|infections]] lead to this [[Complication (medicine)|complication]]. In the United States, [[Hemolytic-uremic syndrome|hemolytic uremic syndrome]] is the principal cause of [[acute kidney failure]] in children, and most cases of [[Hemolytic-uremic syndrome|hemolytic uremic syndrome]] are caused by ''[[Escherichia coli|E. coli]]'' O157:H7.


== Diagnosis ==
== 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 telluride sorbitol-MacConkey agar (CT-SMAC). However, like all cultures, diagnosis is slow using this method, and more rapid diagnosis is possible using [[PCR]] techniques. Newer technologies using [[fluorescent]] and [[antibody]] detection are also under development.
A [[Stool test|stool culture]] can detect the [[Bacteria|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]] [[Telluride (chemistry)|telluride]] [[sorbitol-MacConkey agar]] (CT-SMAC). However, like all cultures, [[diagnosis]] is slow using this method, and more rapid [[diagnosis]] is possible using [[PCR]] techniques. Newer technologies using [[fluorescent]] and [[antibody]] detection are also under development.


===Surveillance===
===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.
''[[Escherichia coli|E. coli]]'' O157:H7 [[infection]] is nationally reportable in the USA and Great Britain. [[hemolytic-uremic syndrome]] is also reportable in most US states.


== Treatment ==
== 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
Most people recover without [[antibiotic]]s or other specific treatment in 5-10 days. There is no [[evidence]] that [[Antibiotic|antibiotics]] improve the course of [[disease]], and it is thought that treatment with some [[Antibiotic|antibiotics]] may precipitate [[kidney]] [[Complication (medicine)|complications]].<ref>{{cite journal
   | last = Walterspiel
   | last = Walterspiel
   | first = J. N.
   | first = J. N.
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   | url = http://www.springerlink.com/content/gn87605160632v3k/
   | url = http://www.springerlink.com/content/gn87605160632v3k/
   | id =  
   | id =  
   | accessdate = 200-01-07 }}</ref> Antidiarrheal agents, such as [[loperamide]] (imodium), should also be avoided.
   | accessdate = 200-01-07 }}</ref> [[Antidiarrhoeal|Antidiarrheal]] agents, such as [[loperamide|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%.
[[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|hemolytic uremic syndrome]] is 3%–5%.


== Prognosis ==
== 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.
The majority of [[Infection|infections]] resolve completely. Those who develop [[Hemolytic-uremic syndrome|hemolytic uremic syndrome]] suffer more long-term consequences. 3–5% of those with [[Hemolytic-uremic syndrome|HUS]] die, causing about 61 deaths annually in the USA. One third of this group have abnormal [[Renal function|kidney function]] many years later, and a few require long-term [[dialysis]]. Another 8% of this group develop other lifelong [[Complication (medicine)|complications]], such as high [[blood pressure]], [[seizure]]s, [[blindness]], [[paralysis]], and, if [[surgery]] is required to remove part of the [[Intestine|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.
There are currently long term studies continuing in Walkerton, Ontario, looking at the long term effects of ''[[Escherichia coli|E. coli]]'' O157:H7 after approximately 2500 people were [[Infection|infected]] through the municipal water system in May 2000.


=== Costs ===
=== 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.
The [[pathogen]] results in an estimated 2,100 [[Hospital|hospitalizations]] annually in the United States. The [[illness]] is often [[Diagnosis|misdiagnosed]]; therefore, expensive and invasive [[Diagnosis|diagnostic]] procedures may be performed. [[Patient|Patients]] who develop [[Hemolytic-uremic syndrome|HUS]] often require prolonged [[Hospital|hospitalization]], [[dialysis]], and long-term follow-up.


== Prevention ==
== Prevention ==
===Agricultural===
===Agricultural===
Beef processing is the most common point of contamination, when during the slaughtering process the contents of intestines 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 more likely to be a source of infection than steak.  In steak only the surface area of a cut is exposed during rendering, 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.
[[Beef]] processing is the most common point of contamination, when during the cattle harvest the contents of [[intestine]] mix with the meat and [[bacteria]] then flourish in the warm, moist conditions. If the [[Infection|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 more likely to be a source of [[infection]] than steak.  In steak, only the surface area of a cut is exposed during rendering, 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 [[Infection|infect]] an entire lot of ground beef.


Accordingly, elimination of infection is unlikely until preventative measures either reduce the number of cattle that carry ''E.coli'' O157:H7 or reduce the contamination of meat during slaughter and grinding.
Accordingly, elimination of [[infection]] is unlikely until preventative measures either reduce the number of cattle that carry ''[[Escherichia coli|E.coli]]'' O157:H7 or reduce the contamination of meat during harvest 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>
In January 2007, Canadian bio-pharmaceutical company Bioniche announced development of 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===
===Culinary and dietary===
Cooking all ground beef and hamburger thoroughly, using a digital instant-read 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).
Cooking all ground beef and hamburger thoroughly, using a digital instant-read meat [[thermometer]], will eliminate the [[organism]]. Ground beef should be cooked until a [[Medical thermometer|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.
When preparing meat, it should be kept separate from other food items. All surfaces and utensils that 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.
Avoid [[Raw milk|unpasteurized milk]], [[juice]], and cider. Commercial [[juice]] is almost always [[Pasteurization|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, immunocompromised persons, and the elderly should avoid eating [[alfalfa]] sprouts until their safety can be assured. Methods to decontaminate alfalfa seeds and sprouts are being investigated.
[[Fruit|Fruits]] and [[Vegetable|vegetables]] should be washed thoroughly, especially those that will not be cooked. Children under 5 years of age, [[Immunodeficiency|immunocompromised]] persons, and the elderly, should avoid eating [[alfalfa]] sprouts until their safety can be assured. Methods to decontaminate alfalfa seeds and sprouts 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.
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.
Proper [[hand washing]] after using the lavatory or changing a [[diaper]], especially among children or those with [[diarrhea]], will reduce the risk of [[Transmission (medicine)|transmission]]. Anyone with a [[Diarrhea|diarrheal illness]] should avoid swimming in public pools or lakes, sharing baths with others, and preparing food for others.


===Opportunities===
===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.
Learning more about the [[ecology]] of this [[organism]] in cattle and other [[Ruminant|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 [[Infection|infections]] would decrease [[Hemolytic-uremic syndrome|HUS]], the major cause of [[Renal insufficiency|kidney failure]] in children in the United States. [[Transmission (medicine)|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])
(''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])

Latest revision as of 19:51, 15 December 2018

Escherichia coli

Scientific classification
Superdomain: Phylogenetica
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Enterobacteriales
Family: Enterobacteriaceae
Genus: Escherichia
Species: E. coli
Binomial name
Escherichia coli
T. Escherich, 1885

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This page is about microbiologic aspects of the organism. For clinical aspects of the disease, see Escherichia coli enteritis.
To view information about other strains of Escherichia coli, see Escherichia coli.

Overview

Escherichia coli O157:H7 is an enterohemorrhagic strain of the bacterium Escherichia coli and a cause of foodborne illness.[1] An estimated 73,000 cases of infection and 61 deaths occur each year in the United States alone.[2] Infection often leads to bloody diarrhea, and occasionally to kidney failure, especially in young Children & elderly people. The infection has been mostly associated with eating under cooked, contaminated ground beef, drinking unpasteurized milk, swimming in or drinking contaminated water, and eating contaminated vegetables. The bacteria can also be spread by person-to-person contact.

Biochemistry

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 flagellar 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. This is one of the hundreds of serotypes of the bacterium Escherichia coli. While most strains are harmless and normally found in the intestine of mammals, this strain which produces Shiga-like toxin, causes severe illness, and is a member of a class of pathogenic E. coli known as enterohemorrhagic Escherichia coli or EHEC. It is sometimes also referred to by its 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 hamburgers, 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.[3]

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 factors (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 sorbitol negative whereas 93% of all E. coli ferment sorbitol.[4] E. coli O157:H7 also lacks the ability to hydrolyze 4-methylumbelliferyl-ß-D-glucuronide (MUG) 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.[5][6]

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 the 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.[7]

Among these virulence factors are a periplasmic catalase and 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.[8] Shiga-like toxins are functionally identical to toxins produced by virulent Shigella species.[9] Strains of E. coli that express Shiga-like toxins gained this ability due to 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.[10][11] 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.[12]

Transmission

The major source of infection is under cooked ground beef; other sources include consumption of unpasteurized milk and juice, raw sprouts, lettuce, and salami, and contact with infected live animals. 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 a small number of cattle farms and can live in the intestine of healthy cattle. The toxin requires highly specific receptors on the cells' surface in order to attach and enter the cell; species such as cattle, swine, and deer that do not carry these receptors, may harbor toxigenic bacteria without any ill effect, shedding them in their feces from where they may spread to humans. Meat can become contaminated during harvest, and organisms can be thoroughly mixed into beef when it is ground. Bacteria present on the cow's udders 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 and smell normal.

Signs and Symptoms

E. coli O157:H7 infection often causes severe, acute bloody diarrhea (although non bloody diarrhea is also possible) and abdominal cramps. Usually little or no 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 hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail. About 2%-7% of infections lead to this complication. In the United States, hemolytic uremic syndrome is the principal cause of acute kidney failure in children, and most cases of hemolytic uremic syndrome are caused by E. coli O157:H7.

Diagnosis

A 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 (SMAC) agar, or the variant cefeximine potassium telluride sorbitol-MacConkey agar (CT-SMAC). However, like all cultures, diagnosis is slow using this method, and more rapid diagnosis is possible using 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. hemolytic-uremic syndrome is also reportable in most US states.

Treatment

Most people recover without antibiotics 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.[13] 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 transfusions 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, seizures, 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 the most common point of contamination, when during the cattle harvest the contents of intestine mix with the meat and bacteria then 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 more likely to be a source of infection than steak. In steak, only the surface area of a cut is exposed during rendering, 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, elimination of infection is unlikely until preventative measures either reduce the number of cattle that carry E.coli O157:H7 or reduce the contamination of meat during harvest and grinding.

In January 2007, Canadian bio-pharmaceutical company Bioniche announced development of a bovine vaccine capable of reducing O157:H7 in cattle by over 99%.[14]

Culinary and dietary

Cooking all ground beef and hamburger thoroughly, using a digital instant-read 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. All surfaces and utensils that 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 pathogens.

Fruits and vegetables should be washed thoroughly, especially those that will not be cooked. Children under 5 years of age, immunocompromised persons, and the elderly, should avoid eating alfalfa sprouts until their safety can be assured. Methods to decontaminate alfalfa seeds and sprouts 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[1], [2])

See also

External links

References

  1. Karch H, Tarr P, Bielaszewska M (2005). "Enterohaemorrhagic Escherichia coli in human medicine". Int J Med Microbiol. 295 (6–7): 405–18. PMID 16238016.
  2. Questions & Answers: Sickness caused by E. coli, Centers for Disease Control and Prevention.
  3. Riley L, Remis R, Helgerson S, McGee H, Wells J, Davis B, Hebert R, Olcott E, Johnson L, Hargrett N, Blake P, Cohen M (1983). "Hemorrhagic colitis associated with a rare Escherichia coli serotype". N Engl J Med. 308 (12): 681–5. PMID 6338386.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. Reisberg, R., S. Olsnes, and K. Eiklid. 1981. The cytotoxic activity of shigella toxin. J. Biol. Chem. 256:8739-8744.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. Walterspiel, J. N. (2003). "Effect of subinhibitory concentrations of antibiotics on extracellular shiga-like toxin I". Infection. 20: 25–29. Retrieved 200-01-07. Unknown parameter |coauthors= ignored (help); Check date values in: |accessdate= (help)
  14. "Canadian Research Collaboration Produces World's First Food Safety Vaccine: Against E. coli 0157:H7". CNX Marketlink. Retrieved 2007-09-15.

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