Verotoxin-producing Escherichia coli
Encyclopedia
Verotoxin-producing Escherichia coli comprise strains of the bacterium Escherichia coli
that, when infecting humans, have been linked with the severe complication hemolytic-uremic syndrome
(HUS). They are known by a number of names, including enterohemorrhagic
E. coli (EHEC), Shiga-like toxin-producing E. coli (STEC or SLTEC), hemolytic uremic syndrome–associated enterohemorrhagic E. coli (HUSEC) and verocytotoxin- or verotoxin-producing E. coli (VTEC).
All these E. coli strains produce Shiga-like toxin
(also known as verotoxin), a major cause of foodborne illness
. These are distinguished from other pathotypes of intestinal pathogenic E. coli including enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC), and diffusely adherent E. coli (DAEC).
The best known of these strains is O157:H7
, but there are non-O157 strains which cause an estimated 36,000 illnesses, 1,000 hospitalizations and 30 deaths in the United States yearly. Food safety specialists recognize "Big Six" strains; O26, O45, O103, O111, O121
, and O145. A 2011 outbreak in Germany is caused by another STEC, O104:H4
. This strain has both enteroaggregative and enterohemorrhagic properties. Both the O145 and O104 strains can cause hemolytic-uremic syndrome, the former strain shown to account for 2% to 51% of known HUS cases; it has been estimated that 56% of such cases are caused by O145 and 14% by other EHEC strains.
EHEC that induces bloody diarrhea leads to HUS in 10% of cases. The clinical manifestations of post-diarrheal HUS include acute renal failure, microangiopathic hemolytic anemia
, and thrombocytopenia
. The verocytotoxin (shiga-like toxin) can directly damage renal and endothelial cells. Thrombocytopenia occurs as platelets are consumed by clotting. Hemolytic anemia results from intravascular fibrin
deposition, increased fragility of red blood cells, and fragmentation.
Antibiotics are of questionable value and have not shown to be of clear clinical benefit. Antibiotics that interfere with DNA synthesis such as fluoroquinolones have been shown to induce the Stx-bearing bacteriophage and cause increased production of toxins. Attempts to block toxin production with antibacterials which target the ribosomal protein synthesis are conceptually more attractive. Plasma exchange
offers a controversial but possibly helpful treatment. The use of antimotility agent
s (medication that suppresses diarrhea by slowing bowel transit) in children under 10 years of age or in elderly patients should be avoided as it increases the risk of HUS with EHEC infections.
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
that, when infecting humans, have been linked with the severe complication hemolytic-uremic syndrome
Hemolytic-uremic syndrome
Hemolytic-uremic syndrome , abbreviated HUS, is a disease characterized by hemolytic anemia, acute renal failure and a low platelet count . It predominantly, but not exclusively, affects children. Most cases are preceded by an episode of diarrhea caused by E. coli O157:H7, which is acquired as a...
(HUS). They are known by a number of names, including enterohemorrhagic
Enterohemorrhagic
Enterohemorrhagic microorganisms are those that, as part of their pathogenesis, cause bloody diarrhea and colitis. While many pathogens are enterohemorrhagic, most cases observed are derived of E. coli serotype O157:H7. The E. coli O104:H4 strain identified as the cause of the 2011 outbreak in...
E. coli (EHEC), Shiga-like toxin-producing E. coli (STEC or SLTEC), hemolytic uremic syndrome–associated enterohemorrhagic E. coli (HUSEC) and verocytotoxin- or verotoxin-producing E. coli (VTEC).
All these E. coli strains produce Shiga-like toxin
Shiga-like toxin
Shiga-like toxin, also known as verotoxin, is a toxin generated by some strains of Escherichia coli . It is named for its similarity to the AB5-type Shiga toxin produced by the bacteria Shigella dysenteriae....
(also known as verotoxin), a major cause of foodborne illness
Foodborne illness
Foodborne illness is any illness resulting from the consumption of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, as well as chemical or natural toxins such as poisonous mushrooms.-Causes:Foodborne illness usually arises from improper handling, preparation, or...
. These are distinguished from other pathotypes of intestinal pathogenic E. coli including enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC), and diffusely adherent E. coli (DAEC).
The best known of these strains is O157:H7
Escherichia coli O157:H7
Escherichia coli O157:H7 is an enterohemorrhagic strain of the bacterium Escherichia coli and a cause of foodborne illness. Infection often leads to hemorrhagic diarrhea, and occasionally to kidney failure, especially in young children and elderly persons...
, but there are non-O157 strains which cause an estimated 36,000 illnesses, 1,000 hospitalizations and 30 deaths in the United States yearly. Food safety specialists recognize "Big Six" strains; O26, O45, O103, O111, O121
Escherichia coli O121
Escherichia coli O121 is a serotype of Escherichia coli, a species of bacteria that lives in the lower intestines of mammals. The presence of many serotypes of E. coli in animals is beneficial or does not cause disease. However, E. coli O121 has been recognized as a potential disease causing...
, and O145. A 2011 outbreak in Germany is caused by another STEC, O104:H4
Escherichia coli O104:H4
Escherichia coli O104:H4 is a rare enterohemorrhagic strain of the bacterium Escherichia coli, and the cause of the 2011 Escherichia coli O104:H4 outbreak...
. This strain has both enteroaggregative and enterohemorrhagic properties. Both the O145 and O104 strains can cause hemolytic-uremic syndrome, the former strain shown to account for 2% to 51% of known HUS cases; it has been estimated that 56% of such cases are caused by O145 and 14% by other EHEC strains.
EHEC that induces bloody diarrhea leads to HUS in 10% of cases. The clinical manifestations of post-diarrheal HUS include acute renal failure, microangiopathic hemolytic anemia
Microangiopathic hemolytic anemia
In medicine microangiopathic hemolytic anemia is a microangiopathic subgroup of hemolytic anemia caused by factors in the small blood vessels. It is identified by the finding of anemia and schistocytes on microscopy of the blood film.-Presentation:It is referred as Runner's anemia...
, and thrombocytopenia
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
. The verocytotoxin (shiga-like toxin) can directly damage renal and endothelial cells. Thrombocytopenia occurs as platelets are consumed by clotting. Hemolytic anemia results from intravascular fibrin
Fibrin
Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....
deposition, increased fragility of red blood cells, and fragmentation.
Antibiotics are of questionable value and have not shown to be of clear clinical benefit. Antibiotics that interfere with DNA synthesis such as fluoroquinolones have been shown to induce the Stx-bearing bacteriophage and cause increased production of toxins. Attempts to block toxin production with antibacterials which target the ribosomal protein synthesis are conceptually more attractive. Plasma exchange
Plasmapheresis
Plasmapheresis is the removal, treatment, and return of blood plasma from blood circulation. It is thus an extracorporeal therapy...
offers a controversial but possibly helpful treatment. The use of antimotility agent
Antimotility agent
Antimotility agents are drugs used to alleviate the symptoms of diarrhea. These include loperamide , diphenoxylate with atropine , and opiates such as paregoric tincture of opium, codeine, and morphine...
s (medication that suppresses diarrhea by slowing bowel transit) in children under 10 years of age or in elderly patients should be avoided as it increases the risk of HUS with EHEC infections.