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The consumption of contaminated food or drinks causes food poisoning. There are different bacteria, viruses or other microbes that cause contamination of food. Sometimes toxic substances also end up in the food causing effect on the normal body functioning. All the microbes and toxic substances that enter the body pass the gastrointestinal tract. Perhaps this explains the reason why most Foodborne diseases have first symptoms, such as nausea, vomiting or diarrhea. According to the World Health Organization, food poisoning remains high cause of deaths in both adults and infants. Therefore, it is crucial to understand the main cause, transmission, symptoms, diagnostic procedures, available treatments, prevention measures, and any other related information. This research focuses on Foodborne illness caused by the bacterium Escherichia coli (E. coli).
OVERVIEW OF THE PATHOGEN E. coli
There are several strains of harmless E. coli living symbiotically along the intestinal tracts of humans as well as other warm-blooded animals. These strains coexist in the bodies of host without causing any disease. Instead, they help in protection of the body against other invading microbes. However, other strains of E. coli cause food poisoning leading to serious problems for humans. The bacteria strains are namely “Shiga toxin-producing” E. coli or STEC because of their associated toxin called Shiga toxin. In the North America, the commonly identified strain of STEC is E. coli 0157:H7. According to Centers for Disease Control and Prevention, E. coli 0157:H7 accounts for approximately 36% of the total infections caused by Shiga toxin-producing E. coli. The main source of E. coli 0157:H7 is cattle but the strain exists in other domestic and wild animals. Apart from the named strain, there are other serotypes of E. coli that cause food poisoning called enterohemorrhagic E. coli. Those that cause diarrhea include Enterotoxigenic E. coli (ETEC) and Enteropathogenic E. coli (EPEC). ETEC is common in the developing world causing bacterial infections, especially to children and travelers. EPEC, on the other hand, causes persistent diarrhea often lasting for two or more weeks. However, there is reduced frequency of infection in developed countries; EPEC remains a significant cause of diarrhea cases.
Strains of E. coli, which produce Shiga toxin, cause E. coli food poisoning. Shiga toxin, together with Shiga-like toxins all fall under protein toxins. These toxins have two units, A and B, which affects the cells and their normal functioning. Firstly, the toxin’s subunit B binds to the cell surface by attaching to glycolipids. This causes subunit A to internalize and enter the cell reaching the cytosol of the cell. The components of Shiga subunit 'A' then binds to ribosome and interferes with them. In this way, the Shiga toxin, disrupts protein synthesis. Shiga toxins can also cause apoptosis through other mechanisms different from the effect on protein synthesis.
Among the wide variety of E. coli bacteria, it is only a few, earlier indicated strains that cause food poisoning. The E. coli that cause poisoning or diarrheas, fall under the strains called enterovirulent E. coli (EEC) strains. These strains either produce toxins or cause intestinal inflammation. There are over 700 serotypes of E. coli, identified either by “O” antigen in their surface or by “H” protein antigens.
Enterohemorrhagic E. coli (EHEC).EHEC produces verocytotoxins VT1 and VT2, which is their main feature. The toxins produced are responsible for both local and systemic disease. EHEC cause both bloody diarrhea, hemorrhagic colitis (HC) and hemorrhagic uraemic syndrome (HUS), commonly among children. The diarrhea is because of adherence and effect of toxin on immediate cells blocking cell’s protein synthesis. When the toxinenters the blood it may travel to the kidney or brain where it binds to receptors on endothelial cells causing HUS. Additionally, VTs cause death of glomerular in the kidney and central nervous system’s endothelial cells in the brain. The most common EHEC serotype is E. coli 0157:H7 but there are other serotypes (0111:H8 and 0104:H21) diarrheogenic to humans. EHEC produces Shiga toxins, so called, because of resemblance to Shigella dysenteriae’s Shiga toxins (Welinder-Olsson and Kaijser 405-416).
Enteropathogenic E. coli (EPEC).EPEC is one of the virotypes of pathogenic E. coli. It causes diarrheal disease that lasts for long. EPEC is a facultative anaerobe lacking fimbriae. This pathogen forms microcolonies on the epithelial cells’ surface in the intestines. EPEC causes lesions because of their adhesion to the gastrointestinal tract using adherence factor. Finally, this strain causes watery and bloody diarrhea especially in developing countries.
Enterotoxigenic E. coli (ETEC).ETEC is a strain of E. coli, characterized by production of heat-labile toxin, heat-stable, or both toxins. EHEC cause disease by colonizing the surface of intestines where they expend their enterotoxins. This strain of E. coli cause watery diarrhea usually lacking blood or mucus. EHEC highly associates with traveler’s diarrhea and diarrhea in children from developing countries as most researches have shown. Diarrhea caused by EHEC has a short duration, usually fewer than five days.
Enteroadherent E. coli (EAEC).EAEC cause persistent watery diarrhea mostly in children and immunosuppressed patients.
Enteroinvasive E. coli (EIEC).This strain of E coli cause watery diarrhea (dysentery). It relates highly to Shigellosis infections. EIEC uses adhesion of proteins to attach to the intestinal wall. However, this strain does not produce toxins; their action is mechanical.
Enteroaggregative E. coli (EAggEC).Diarrhea caused by EAEC is persistent lasting more than fourteen days. The infection is common in developing countries. The strain’s name is aggregative because of its ability to adhere to monolayers of cultured cell with a phenotypically aggregative adhesion (Law and Chart 1).
Food and Drink Transmission. Food poisoning by E. coli occurs when people eat contaminated food or drink infected water. When the bacteria get into the body, they use their infection mechanisms to cause the different types of food poisoning. E. coli infections come from different ways a person comes in contact bacteria, in food, water, or other forms of person-to-person contact. Firstly, there are different ways through which food gets E. coli. During processing of meat, the bacterium can get into the meat. E. coli bacteria can survive in temperatures up to 71 degree Celsius. Therefore, undercooking infected meat causes transmission when a person feeds on the meat. This is the commonest way of transmission in the United States. On the other hand, all the food types exposed to infected meat can acts as a transmission channel. Secondly, E. coli can spread through milk and dairy products. The bacteria in the bloodstream always get into the udder and finally into the milk. Therefore, infection is also possible when raw milk does not boil. Other channels of infection are raw fruits, vegetables, or juices infected with E. coli bacteria.
Transmission through Water. Sometimes E. coli pathogens get into water bodies such as rivers, lakes or pools. The infection of water comes from improper sewage disposal or use of bushes as toilets, especially in poor countries. The pathogens from infected fecal matter may then end up in a person swimming or use the water for domestic use. On the cities, poor treatment of water with chlorine leads to the transfer of transmission of E. coli bacteria.
Person-to-Person Transmission. E. coli can spread if an infected person fails to wash hands after using the toilet. The transferred bacteria easily get into the body if the newly infected person handles food without washing the hands.
After E. coli infects a person, some time elapses, before the first symptoms are seen. It is an incubation period. The average incubation period of E. coli 0157:H7 is approximately three to four days. However, it is imperative to note that while some people may get ill in a day, others go up to ten days (Lew 17). Foodborne disease of E. coli has a range of symptoms, which varies from person to person. Children show signs earlier and more often than adults do. The commonest first symptom is mild stomachache (Schlossberg 49). However, STEC can cause complications such as nausea, severe abdominal pain, diarrhea (watery or bloody depending on causative pathogen), and fatigue. Sometimes, STEC causes mild fever and vomiting (Hayhurst 14). In other instances, E. coli may cause life-threatening disease, with effect on brain and kidney. Haemolytic Uraemic Syndrome (HUS) caused by ETEC leads to renal failure and haemolytic anaemia.
STEC infections diagnosis is through laboratory testing of stool specimens. Other methods can, however, be applied in determining the serotype of the strain. The methods used in the laboratory vary because of the difference in characteristics. E. coli are a normal flora in the body, and this gives the challenge of identification. However, EIEC strains do not ferment lactose (non-lactose fermentors); hence, MacConkey agar can be used in culturing. On the other hand, EHEC uniquely ferments sorbitol slowly thus allowing the use of MacConkey sorbitol agar. E. coli in the bladder and cerebrospinal fluid of CNS identification can use MacConkey agar because these locations are usually free of bacteria (Harvey et al. 114). Immunomagnetic separation assays or the application of polymerase chain reaction (PCR) has enabled detection and separation of different serotypes and genes coding for verotoxins (enterotoxigenic E. coli) respectively (O’Connor 91). Clinical diagnosis, which involves questioning the patient and this only, applies when the laboratory diagnosis is impossible (Fratamico 363).
E. coli infections usually disappear on its own after some time. However, it is crucially necessary to take a lot of water. Diarrhea causes lose of body fluids, and this can result in dehydration. Dehydration is extremely dangerous especially to babies, small children, and elderly people. Bloody diarrhea indicates inflammation and infection of the intestinal walls. Arguably, it is risky to take antibiotics because it can slow digestion; hence, allowing additional time for poisons from E. coli to enter the body. Consequently, antibiotics can lead to increased risk of Hemolytic Uremic Syndrome (HUS), which can end in kidney failure. In other situations, losing a lot of blood due to E. coli infection, calls for blood transfusion may be necessary. Dialysis also helps in dealing with a kidney infection.
Prevention of E. coli infection involves stoppage or reduction of the transfer of pathogen from food, animals, another person, and drinks in reaching human being. Always wash hands thoroughly after using the bathroom or changing diapers. Coupling high maintenance of hygiene in the animal houses and washing hands after handling animals helps a lot. It is necessary to cook all the food proper, especially the meat from animal products. Wash all the fruits, vegetables and always avoid unpasteurized milk or juices. In order to reduce kitchen cross contamination, all the cooked food should never mix with uncooked food. Finally, it is essential to boil water before drinking (Trickett 54).
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