|Escherichia coli O157:H7|
|Topographical images of colonies of E. coli O157:H7 strains (A) 43895OW ( curli non-producing) and (B) 43895OR (curli producing) grown on agar for 48 h at 28°C.|
|Classification and external resources|
Escherichia coli O157:H7 is a serotype of the bacterial species Escherichia coli and is one of the Shiga toxin–producing types of E. coli. It is a cause of disease, typically foodborne illness, through consumption of contaminated and raw food, including raw milk and undercooked ground beef.Infection with this type of pathogenic bacteria may lead to hemorrhagic diarrhea, and to kidney failure; these have been reported to cause the deaths of children younger than five years of age, of elderly patients, and of patients whose immune systems are otherwise compromised.
A serotype or serovar is a distinct variation within a species of bacteria or virus or among immune cells of different individuals. These microorganisms, viruses, or cells are classified together based on their cell surface antigens, allowing the epidemiologic classification of organisms to the sub-species level. A group of serovars with common antigens is called a serogroup or sometimes serocomplex.
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.
Escherichia coli, also known as E. coli, is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in their hosts, and are occasionally responsible for product recalls due to food contamination. The harmless strains are part of the normal microbiota of the gut, and can benefit their hosts by producing vitamin K2, and preventing colonization of the intestine with pathogenic bacteria, having a symbiotic relationship. E. coli is expelled into the environment within fecal matter. The bacterium grows massively in fresh fecal matter under aerobic conditions for 3 days, but its numbers decline slowly afterwards.
Transmission is via the fecal–oral route, and most illness has been through distribution of contaminated raw leaf green vegetables, undercooked meat and raw milk.
The fecal–oral route describes a particular route of transmission of a disease wherein pathogens in fecal particles pass from one person to the mouth of another person. Main causes of fecal–oral disease transmission include lack of adequate sanitation, and poor hygiene practices. If soil or water bodies are polluted with fecal material, humans can be infected with waterborne diseases or soil-transmitted diseases. Fecal contamination of food is another form of fecal-oral transmission. Washing hands properly after changing a baby's diaper or after performing anal hygiene can prevent foodborne illness from spreading.
E. coli O157:H7 infection often causes severe, acute hemorrhagic diarrhea (although nonhemorrhagic 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 sometimes be asymptomatic.
A cramp is a sudden, involuntary muscle contraction or over-shortening; while generally temporary and non-damaging, they can cause significant pain, and a paralysis-like immobility of the affected muscle. Onset is usually sudden, and it resolves on its own over a period of several seconds, minutes or hours. Cramps may occur in a skeletal muscle or smooth muscle. Skeletal muscle cramps may be caused by muscle fatigue or a lack of electrolytes such as low sodium, low potassium or low magnesium. Cramps of smooth muscle may be due to menstruation or gastroenteritis.
In medicine, a disease is considered asymptomatic if a patient is a carrier for a disease or infection but experiences no symptoms. A condition might be asymptomatic if it fails to show the noticeable symptoms with which it is usually associated. Asymptomatic infections are also called subclinical infections. Other diseases might be considered subclinical if they present some but not all of the symptoms required for a clinical diagnosis. The term clinically silent is also used.
In some people, particularly children under five years of age, persons whose immunologies are otherwise compromised, and the elderly, the infection can cause hemolytic uremic syndrome (HUS), 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, HUS is the principal cause of acute kidney failure in children, and most cases of HUS are caused by E. coli O157:H7.
Red blood cells, also known as RBCs, red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes (from Greek erythros for "red" and kytos for "hollow vessel", with -cyte translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, and release it into tissues while squeezing through the body's capillaries.
Strains of E. coli that express Shiga and Shiga-like toxins gained this ability due to infection with a prophage containing the structural coding for the toxin, and nonproducing strains may become infected and produce shiga-like toxins after incubation with shiga toxin positive strains. The prophage responsible seems to have infected the strain's ancestors fairly recently, as viral particles have been observed to replicate in the host if it is stressed in some way (e.g. antibiotics).
Shigatoxigenic Escherichia coli (STEC) and verotoxigenic E. coli (VTEC) are strains of the bacterium Escherichia coli that produce either Shiga toxin or Shiga-like toxin (verotoxin). Only a minority of the strains cause illness in humans. The ones that do are collectively known as enterohemorrhagic E. coli (EHEC) and are major causes of foodborne illness. When infecting humans, they often cause gastroenteritis, enterocolitis, and bloody diarrhea and sometimes cause a severe complication called hemolytic-uremic syndrome (HUS). The group and its subgroups are known by various names. They are distinguished from other strains 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).
Transduction is the process by which foreign DNA is introduced into a cell by a virus or viral vector. An example is the viral transfer of DNA from one bacterium to another and hence an example of horizontal gene transfer. Transduction does not require physical contact between the cell donating the DNA and the cell receiving the DNA, and it is DNase resistant. Transduction is a common tool used by molecular biologists to stably introduce a foreign gene into a host cell's genome.
A prophage is a bacteriophage genome inserted and integrated into the circular bacterial DNA chromosome or existing as an extrachromosomal plasmid. This is a latent form of a phage, in which the viral genes are present in the bacterium without causing disruption of the bacterial cell. Pro means ''before'', so, prophage means the stage of a virus in the form of genome inserted into host DNA before attaining its real form inside host.
All clinical isolates of E. coli O157:H7 possess the plasmid pO157.The periplasmic catalase is encoded on pO157 and may enhance the virulence of the bacterium by providing additional oxidative protection when infecting the host. E. coli O157:H7 non-hemorrhagic strains are converted to hemorrhagic strains by lysogenic conversion after a bacteriophage infection to non-hemorrhagic cells.
Catalase is a common enzyme found in nearly all living organisms exposed to oxygen. It catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS). Likewise, catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert millions of hydrogen peroxide molecules to water and oxygen each second.
While it is relatively uncommon, the E. coli serotype O157:H7 can naturally be found in the intestinal contents of some cattle, goats, and even sheep.The digestive tract of cattle lack the Shiga toxin receptor globotriaosylceramide, and thus, these can be asymptomatic carriers of the bacterium. The prevalence of E. coli O157:H7 in North American feedlot cattle herds ranges from 0 to 60%. Some cattle may also be so-called “super-shedders” of the bacterium. Super-shedders may be defined as cattle exhibiting rectoanal junction colonization and excreting >103 to 4 CFU g−1 feces. Super-shedders have been found to constitute a small proportion of the cattle in a feedlot (<10%) but they may account for >90% of all E. coli O157:H7 excreted.
Infection with E. coli O157:H7 follows ingestion of contaminated food or water, or oral contact with contaminated surfaces. Examples of this can be undercooked ground beef but also leafy vegetables and raw milk. Fields often get contaminated with the bacterium through irrigation processes or contaminated water naturally entering the soil.It is highly virulent, with a low infectious dose: an inoculation of fewer than 10 to 100 CFU of E. coli O157:H7 is sufficient to cause infection, compared to over one-million CFU for other pathogenic E. coli strains.
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 cefixime potassium tellurite sorbitol-MacConkey agar (CT-SMAC). On SMAC agar O157 colonies appear clear due to their inability to ferment sorbitol, while the colonies of the usual sorbitol-fermenting serotypes of E. coli appear red. Sorbitol nonfermenting colonies are tested for the somatic O157 antigen before being confirmed as E. coli O157. Like all cultures, diagnosis is time-consuming with this method; swifter diagnosis is possible using quick E. coli DNA extraction method plus PCR techniques. Newer technologies using fluorescent and antibody detection are also under development.
E. coli O157:H7 infection is nationally reportable in the USA, Great Britain, and Germany and is reportable in most US states. It is also reportable in most states of Australia including Queensland.
While fluid replacement and blood pressure support may be necessary to prevent death from dehydration, most victims recover without treatment in five to 10 days. There is no evidence that antibiotics improve the course of disease, and treatment with antibiotics may precipitate hemolytic uremic syndrome.The antibiotics are thought to trigger prophage induction, and the prophages released by the dying bacteria infect other susceptible bacteria, converting them into toxin-producing forms. Antidiarrheal agents, such as loperamide (imodium), should also be avoided as they may prolong the duration of the infection.
Certain novel treatment strategies, such as the use of anti-induction strategies to prevent toxin productionand the use of anti-Shiga toxin antibodies, have also been proposed.
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 followup.
Proper hand washing after using the lavatory or changing a diaper, especially among children or those with diarrhea, reduces 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 and even avoiding raw milk.[ citation needed ]
The U.S.D.A. banned the sale of ground beef contaminated with the O157:H7 strain in 1994.
Shigellosis is an infection of the intestines caused by Shigella bacteria. Symptoms generally start one to two days after exposure and include diarrhea, fever, abdominal pain, and feeling the need to pass stools even when the bowels are empty. The diarrhea may be bloody. Symptoms typically last five to seven days. Complications can include reactive arthritis, sepsis, seizures, and hemolytic uremic syndrome.
Shigella is a genus of Gram-negative, facultative aerobic, non-spore-forming, nonmotile, rod-shaped bacteria genetically closely related to E. coli. The genus is named after Kiyoshi Shiga, who first discovered it in 1897.
Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, expressed by genes considered to be part of the genome of lambdoid prophages. The toxins are named after Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by Shigella dysenteriae. Shiga-like toxin (SLT) is a historical term for similar or identical toxins produced by Escherichia coli. The most common sources for Shiga toxin are the bacteria S. dysenteriae and the some serotypes of Escherichia coli (STEC), which includes serotypes O157:H7, and O104:H4.
Hemolytic-uremic syndrome (HUS) is a group of blood disorders characterized by low red blood cells, acute kidney failure, and low platelets. Initial symptoms typically include bloody diarrhea, fever, vomiting, and weakness. Kidney problems and low platelets then occur as the diarrhea is improving. While children are more commonly affected adults may have worse outcomes. Complications may include neurological problems and heart failure.
Romaine or cos lettuce is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. Unlike most lettuces, it is tolerant of heat. In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together.
Lysogeny, or the lysogenic cycle, is one of two cycles of viral reproduction. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formations of a circular replicon in the bacterial cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and at later events can release it, causing proliferation of new phages via the lytic cycle. Lysogenic cycles can also occur in eukaryotes, although the method of DNA incorporation is not fully understood.
Sorbitol MacConkey agar is a variant of traditional MacConkey agar used in the detection of E. coli O157:H7. Traditionally, MacConkey agar has been used to distinguish those bacteria that ferment lactose from those that do not. This is important because gut bacteria, such as Escherichia coli, can typically ferment lactose, while important gut pathogens, such as Salmonella enterica and most shigellas are unable to ferment lactose. Shigella sonnei can ferment lactose, but only after prolonged incubation, so it is referred to as a late-lactose fermenter.
The AB5 toxins are six-component protein complexes secreted by certain pathogenic bacteria known to cause human diseases such as cholera, dysentery, and hemolytic-uremic syndrome. One component is known as the A subunit, and the remaining five components are B subunits. All of these toxins share a similar structure and mechanism for entering targeted host cells. The B subunit is responsible for binding to receptors to open up a pathway for the A subunit to enter the cell. The A subunit is then able to use its catalytic machinery to take over the host cell's regular functions.
Escherichia coli O121 is a pathogenic serotype of Escherichia coli, associated with Shiga toxin, intestinal bleeding, and hemolytic-uremic syndrome (HUS). HUS, if left untreated, can lead to kidney failure.
Escherichia coli O104:H21 is a rare 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 in animals. However, some serotypes of E. coli have been recognized as pathogenic to humans, e.g. E. coli O157:H7, E. coli O121 and E. coli O104:H21.
Enteroinvasive Escherichia coli (EIEC) is a type of pathogenic bacteria whose infection causes a syndrome that is identical to shigellosis, with profuse diarrhea and high fever. EIEC are highly invasive, and they use adhesin proteins to bind to and enter intestinal cells. They produce no toxins, but severely damage the intestinal wall through mechanical cell destruction.
A novel strain of Escherichia coli O104:H4 bacteria caused a serious outbreak of foodborne illness focused in northern Germany in May through June 2011. The illness was characterized by bloody diarrhea, with a high frequency of serious complications, including hemolytic-uremic syndrome (HUS), a condition that requires urgent treatment. The outbreak was originally thought to have been caused by an enterohemorrhagic (EHEC) strain of E. coli, but it was later shown to have been caused by an enteroaggregative E. coli (EAEC) strain that had acquired the genes to produce Shiga toxins, present in organic fenugreek sprouts.
Escherichia coli O104:H4 is an enteroaggregative Escherichia coli strain of the bacterium Escherichia coli, and the cause of the 2011 Escherichia coli O104:H4 outbreak. The "O" in the serological classification identifies the cell wall lipopolysaccharide antigen, and the "H" identifies the flagella antigen.
Escherichia coli ( Anglicized to ; commonly abbreviated E. coli) is a gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some serotypes are pathogenic and can cause serious food poisoning in humans, and are occasionally responsible for product recalls. E. coli are also responsible for a majority of cases of urinary tract infections. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K2, and by preventing the establishment of pathogenic bacteria within the intestine.
Enteroaggregative Escherichia coli are a pathotype of Escherichia coli associated with acute and chronic diarrhea in both the developed and developing world. EAEC are defined by their "stacked-brick" pattern of adhesion to the human laryngeal epithelial cell line HEp-2. The pathogenesis of EAEC involves the aggregation of and adherence of the bacteria to the intestinal mucosa, where they elaborate enterotoxins and cytotoxins that damage host cells and induce inflammation that results in diarrhea.
Clostridioides difficile, also known as C. difficile, C. diff, or sometimes CDF/cdf, is a species of Gram-positive spore-forming bacterium.
The 2015 United States E. coli outbreak is an incident in the United States involving the spread of Escherichia coli O157:H7 through contaminated celery which was consumed in chicken salad at various large retailers. A product recall covering more than one dozen states and over 155,000 products has taken place as a result of the incident.
After the U.S.D.A. banned the O157 form of E. coli from ground beef in 1994, the meat industry sued to block the move, but the agency prevailed in court.