E. coli virotypes Food Poisoning, Infection and Illness

Escherichia coli (E. coli) is a type of bacteria that belongs to the family Enterobacteriaceae, which includes many other common and diverse bacteria such as Salmonella, Shigella, Klebsiella and Yersinia. E. coli is normally found in the lower intestine of warm-blooded animals, including humans, where it plays a vital role in digestion and immunity. E. coli is also widely used as a model organism in biotechnology and microbiology, where it has been the host for most of the work with recombinant DNA and genetic engineering.

However, not all strains of E. coli are harmless or beneficial. Some strains have acquired virulence factors that enable them to cause various diseases in humans and animals, ranging from mild diarrhea to life-threatening infections. These pathogenic strains are classified into different groups based on their mode of transmission, their mechanism of infection and their clinical manifestations. Some of the most important groups are:

• Enterotoxigenic E. coli (ETEC), which produces toxins that cause watery diarrhea, especially in travelers and children in developing countries.
• Enteropathogenic E. coli (EPEC), which adheres to and damages the intestinal cells, causing diarrhea and vomiting in infants and young children.
• Enterohemorrhagic E. coli (EHEC), which produces Shiga toxins that cause bloody diarrhea and hemolytic uremic syndrome (HUS), a serious complication that affects the kidneys and blood cells.
• Enteroinvasive E. coli (EIEC), which invades and destroys the intestinal cells, causing dysentery-like symptoms similar to those of Shigella infection.
• Enteroaggregative E. coli (EAEC), which forms aggregates on the intestinal cells and produces toxins that cause persistent diarrhea in children and adults.
• Diffusely adherent E. coli (DAEC), which attaches diffusely to the intestinal cells and causes watery diarrhea, mostly in children.

E. coli infections are usually transmitted through the fecal-oral route, meaning that the bacteria are shed in the feces of infected animals or humans and contaminate food, water or other objects that are ingested by susceptible hosts. Some of the common sources of contamination are:

• Undercooked or raw meat, especially ground beef, that contains EHEC or other pathogenic strains.
• Unpasteurized milk or dairy products that are contaminated with EHEC or other pathogenic strains.
• Fruits and vegetables that are irrigated or washed with contaminated water or fertilized with animal manure that contains EHEC or other pathogenic strains.
• Drinking water that is polluted with animal or human feces that contains EHEC or other pathogenic strains.
• Direct contact with animals or humans that carry EHEC or other pathogenic strains in their intestines.

The symptoms of E. coli infection vary depending on the strain and the host factors, but they usually include diarrhea, abdominal cramps, nausea, vomiting and fever. In some cases, complications such as dehydration, kidney failure, blood clots, seizures or death may occur. The diagnosis of E. coli infection is based on the isolation and identification of the bacteria from stool samples or other specimens using culture methods or molecular techniques. The treatment of E. coli infection depends on the severity of the illness and the type of strain involved, but it usually involves supportive care such as fluid replacement and symptomatic relief. Antibiotics are not always effective or recommended for E. coli infection, as they may increase the risk of HUS or induce resistance in some strains. Prevention of E. coli infection relies on proper hygiene practices such as washing hands before eating or preparing food, cooking meat thoroughly, avoiding raw or unpasteurized dairy products, washing fruits and vegetables before consumption, boiling or treating drinking water if its quality is doubtful, and avoiding contact with sick animals or humans.

E. coli is a versatile and adaptable bacterium that can be both a friend and a foe to humans and animals. It is important to understand its biology, diversity and pathogenicity in order to prevent and treat its infections effectively.

E. coli (Escherichia coli) is a type of bacteria that belongs to the family Enterobacteriaceae and the genus Escherichia. It is a Gram-negative, rod-shaped, facultative anaerobic bacterium that can grow and survive in various environments.

Some of the main characteristics of E. coli are:

• It is non-spore forming, meaning it does not produce dormant cells that can resist harsh conditions.
• It is flagellated, meaning it has long, whip-like structures that help it move and swim.
• It can grow in a range of temperatures from 4°C to 45°C, but its optimal temperature is 37°C, which is the normal body temperature of humans and animals.
• It can survive at low pH levels as acidic as 3.6, which is similar to the pH of vinegar.
• It can survive in fermentation and drying processes, which are often used to preserve food products.
• It can use oxygen as an electron acceptor (aerobic respiration) or other substances such as nitrate or fumarate (anaerobic respiration) depending on the availability of oxygen. It can also ferment sugars such as glucose and lactose to produce acids and gases.
• It has a circular chromosome that contains about 4.6 million base pairs of DNA and encodes about 4,400 genes. It also has plasmids, which are small circular pieces of DNA that can carry extra genes such as antibiotic resistance or toxin production.
• It has a cell wall composed of a thin layer of peptidoglycan and an outer membrane that contains lipopolysaccharides (LPS), which are complex molecules that trigger immune responses in humans and animals. The LPS also determines the antigenic properties of E. coli, which are used to classify different strains based on their O (somatic), H (flagellar) and K (capsular) antigens.

E. coli is one of the most diverse and versatile bacteria, with hundreds of strains that have different genetic traits and phenotypic features. Most strains are harmless or beneficial to humans and animals, as they are part of the normal microbiota of the gut and perform functions such as producing vitamin K2 or preventing the colonization of pathogenic bacteria. However, some strains are pathogenic and can cause serious infections and diseases such as diarrhea, urinary tract infections, septicemia, pneumonia and meningitis. These strains have acquired virulence factors such as toxins, adhesins, invasins and siderophores that enable them to attach to host cells, damage tissues, evade immune defenses and obtain nutrients.

E. coli is widely used as a model organism in biological research, as it is easy to grow and manipulate in the laboratory. It has also been extensively studied for its physiology, metabolism, genetics and evolution. Moreover, it has been exploited for biotechnology applications such as producing recombinant proteins, enzymes, vaccines and biofuels. E. coli is also an important indicator organism for fecal contamination in water and food samples, as it can be detected by simple tests such as culture or PCR. However, E. coli also poses a public health threat due to its potential to cause outbreaks of foodborne illness or waterborne disease through contaminated sources or poor hygiene practices. Therefore, it is essential to monitor and control the presence and spread of E. coli in various environments and prevent its transmission to humans and animals.

E. coli are the normal intestinal microflora of warm-blooded animals and are transmitted via the fecal-oral route. Cattle, sheep, goats, giraffes, camels, dogs, cats and swine are the major reservoir of Shiga-toxin E. coli (STEC), a type of E. coli that can cause severe illness . Humans are infected through contaminated water, fruits, vegetables, meat (especially ground beef) and fish (finfish and shellfish) .

Fruits and vegetables are frequently contaminated from the water and soil and also from the untreated manures which are used as biofertilizers for the plants. Contamination of pathogen occurs frequently during slaughtering of meat through fecal contact, cross-contamination, unhygienic processing of food products. Direct human to animal contact or human to human contact can also transmit the disease.

Some foods that have been associated with most outbreaks of E. coli food poisoning are :

• Ground beef, ground bison, hamburgers, dried salami
• Sprouts (alfalfa sprouts, radish sprouts and clover sprouts)
• Unpasteurized dairy (raw milk, yoghurt, unpasteurized cheese, ice cream)
• Fruit and vegetables (lettuce, coleslaw, cucumbers, spinach, raw apple cider)
• Water (drinking water, recreational water)

To prevent E. coli food poisoning, it is important to practice good hygiene and food safety measures such as washing hands before and after handling food, cooking meat thoroughly, avoiding cross-contamination of raw and cooked foods, refrigerating leftovers promptly, drinking only pasteurized milk and juice and using clean water for drinking and washing . Travelers should also be careful about what they eat and drink in areas where sanitation is poor.

E. coli food poisoning is a serious public health problem that affects millions of people worldwide every year. According to the U.S. Food and Drug Administration (FDA), each year E. coli causes an estimated 265,000 illnesses, 3,600 hospitalizations, and 30 deaths in the United States. The Centers for Disease Control and Prevention (CDC) reports that in 2021, there were four outbreaks of E. coli infections linked to packaged salads, baby spinach, cake mix, and an unknown food source.

Different types of E. coli tend to contaminate different types of foods and water. Previous U.S. outbreaks of pathogenic E. coli have included leafy greens, sprouts, raw milk and cheeses, and raw beef and poultry. Some wildlife, livestock, and humans are occasional carriers of pathogenic E. coli and can contaminate meats and food crops. Ruminant animals such as cattle, goats, sheep, deer or elk, as well as other animals such as pigs or birds are known carriers of Shiga toxin-producing E. coli (STEC), which is the most common and severe type of E. coli that causes food poisoning.

The global distribution of E. coli food poisoning varies depending on the region, climate, sanitation, and food safety practices. In developing countries, especially in tropical and subtropical areas, E. coli food poisoning is more prevalent and causes more deaths than in developed countries. This is because of the lack of access to clean water, proper hygiene, and adequate health care facilities. Children under five years old are particularly vulnerable to E. coli infection and its complications such as hemolytic uremic syndrome (HUS), which is a life-threatening condition that affects the kidneys and blood cells.

In recent years, the emergence of new strains of E. coli that are more virulent and resistant to antibiotics has posed a major challenge for the prevention and control of food poisoning outbreaks. For example, in 2011, a large outbreak of E. coli O104:H4 occurred in Germany and other European countries, affecting more than 4,000 people and causing 50 deaths. This strain was unusual because it combined the characteristics of two different types of E. coli: enteroaggregative E. coli (EAEC), which causes persistent diarrhea; and STEC, which produces Shiga toxin that damages the intestinal lining and blood vessels. The source of this outbreak was traced to fenugreek sprouts imported from Egypt.

The prevention and control of E. coli food poisoning requires a collaborative effort from various stakeholders along the food supply chain, from farm to fork. This includes implementing good agricultural practices, ensuring proper hygiene and sanitation, monitoring water quality and soil amendments, avoiding cross-contamination during processing and handling, cooking food thoroughly before consumption, educating consumers about food safety risks and behaviors, and conducting surveillance and outbreak investigations to identify and contain sources of contamination . By following these measures, the incidence and severity of E. coli food poisoning can be reduced and public health can be protected.

Intestinal pathogenic E. coli (IPEC) are a group of E. coli strains that cause diarrhea and other intestinal diseases in humans and animals. IPEC are classified into six main pathotypes based on their virulence factors and mechanisms of infection :

• Enterotoxigenic E. coli (ETEC)
• Enteropathogenic E. coli (EPEC)
• Enterohemorrhagic E. coli (EHEC)
• Enteroinvasive E. coli (EIEC)
• Enteroaggregative E. coli (EAEC)
• Diffusely adherent E. coli (DAEC)

Each pathotype has its own distinctive features, clinical manifestations and epidemiology . Here is a brief overview of each pathotype:

Enterotoxigenic E. coli (ETEC)

• ETEC is the most common cause of traveler`s diarrhea and a major cause of diarrhea in children in developing countries .
• ETEC produces either heat-labile enterotoxin (LT) or heat-stable enterotoxin (ST) or both, which stimulate fluid secretion in the intestinal cells and cause watery diarrhea .
• ETEC also produces fimbriae or pili that help them attach to the intestinal epithelium and colonize the small intestine .
• Symptoms of ETEC infection include fever, abdominal cramps, nausea and watery diarrhea that may last for several days .
• ETEC infection is usually self-limiting and can be treated with oral rehydration therapy and antibiotics if needed .

Enteropathogenic E. coli (EPEC)

• EPEC is mainly associated with diarrhea in infants and young children in developing countries, especially where sanitation is poor .
• EPEC does not produce toxins but causes damage to the intestinal cells by attaching and effacing (A/E) lesions, which disrupt the microvilli and impair nutrient absorption .
• EPEC also injects effector proteins into the host cells through a type III secretion system, which modulate host cell signaling and immune responses .
• Symptoms of EPEC infection include diarrhea, abdominal cramps, vomiting, fever and dehydration that may be severe and persistent .
• EPEC infection can be treated with oral rehydration therapy and antibiotics if needed .

Enterohemorrhagic E. coli (EHEC)

• EHEC is the most virulent pathotype of IPEC and can cause serious complications such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS) .
• EHEC produces Shiga toxins (Stx) that inhibit protein synthesis and induce apoptosis in the intestinal cells, leading to bloody diarrhea and inflammation .
• EHEC also causes A/E lesions similar to EPEC but with a different type of fimbriae called intimin .
• Symptoms of EHEC infection include bloody diarrhea, abdominal cramps, vomiting, fever and sometimes hematuria (blood in urine) .
• In some cases, especially in children under 5 years old and elderly people, EHEC infection can lead to HUS, which is characterized by hemolytic anemia, thrombocytopenia and acute kidney failure[^2

To diagnose illness caused by E. coli infection, doctors usually send a sample of the patient`s stool to a laboratory to test for the presence of E. coli bacteria and the toxins they produce. The stool sample should be collected in a sterile container and sent to the laboratory as soon as possible.

Depending on the type and severity of the infection, different methods can be used to identify and characterize the E. coli strains. Some of the common methods are:

• Culture: The stool sample is inoculated on selective and differential media, such as MacConkey agar, eosin methylene blue agar, sorbitol MacConkey agar or cystine-lactose electrolyte-deficient agar . These media allow the growth of gram-negative bacteria and distinguish between lactose-fermenting and non-lactose-fermenting colonies. E. coli usually appear as pink colonies on MacConkey agar, green metallic colonies on eosin methylene blue agar, colorless colonies on sorbitol MacConkey agar (for EHEC) and yellow colonies on cystine-lactose electrolyte-deficient agar. The colonies can be further tested for biochemical reactions, such as indole production, citrate utilization, urease activity and motility.

• Serotyping: The E. coli strains can be classified into different serotypes based on their antigenic properties. The most important antigens are O (somatic), H (flagellar) and K (capsular). For example, E. coli O157:H7 is a serotype that has O157 somatic antigen and H7 flagellar antigen. Serotyping can be done by using specific antisera that agglutinate with the corresponding antigens on the bacterial surface.

• Toxin assays: Some E. coli strains produce toxins that cause diarrhea and other complications. These toxins can be detected by using various assays, such as enzyme immunoassays, latex agglutination tests, polymerase chain reaction (PCR) or cell culture assays . For example, Shiga toxin-producing E. coli (STEC) can be identified by using an enzyme immunoassay that detects the presence of Shiga toxin in the stool sample or by using a PCR assay that amplifies the genes encoding Shiga toxin.

• Molecular typing: Molecular methods can be used to determine the genetic relatedness and diversity of E. coli strains. These methods include pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), multiple-locus variable-number tandem-repeat analysis (MLVA) or whole-genome sequencing (WGS) . These methods can help in epidemiological investigations, outbreak detection and source tracing of E. coli infections .

The choice of diagnostic method depends on the availability of resources, the turnaround time and the clinical relevance of the results. The laboratory diagnosis of E. coli infections can help in guiding appropriate treatment and prevention strategies.

E. coli food poisoning is usually a self-limiting illness that resolves within a few days. However, some cases may require medical attention and treatment, especially if there are signs of dehydration, bloody diarrhea, severe abdominal pain, fever or complications such as hemolytic uremic syndrome (HUS) or kidney failure.

The following are some of the treatment and control measures for E. coli food poisoning:

• Fluids: It is important to drink plenty of fluids to stay hydrated and replenish electrolytes, such as sodium and potassium, that are lost due to diarrhea and vomiting . Oral rehydration solutions (ORS) are available over-the-counter or can be made at home by mixing 6 teaspoons of sugar and 1/2 teaspoon of salt in 1 liter of clean water.
• Rest: It is advisable to rest and avoid physical activity to conserve energy and allow the body to heal.
• Diet: It is recommended to eat bland and easy-to-digest foods, such as rice, bananas, toast, applesauce and yogurt, and avoid spicy, fatty, fried or dairy foods that may worsen the symptoms . Gradually resume a normal diet as the symptoms improve.
• Antibiotics: Antibiotics are not routinely prescribed for E. coli food poisoning, as they may not be effective or may increase the risk of HUS in some cases . However, doctors may prescribe antibiotics such as rifaximin or rifamycin for adults with travelers` diarrhea caused by certain strains of E. coli who do not have fever or blood in the stool. Antibiotics may also be given for severe or complicated infections, such as septicemia or meningitis .
• Antidiarrheals: Antidiarrheal medications, such as loperamide or bismuth subsalicylate, may help reduce the frequency and severity of diarrhea . However, they should be used with caution and only under a doctor`s advice, as they may slow down the clearance of the bacteria from the intestines or worsen the symptoms in some cases .
• Hospitalization: In some cases, hospitalization may be required for intravenous fluids, blood transfusions, dialysis or other supportive care for severe dehydration, HUS or other complications .

To prevent E. coli food poisoning, the following preventive measures should be followed:

• Food safety: Food safety practices should be observed at all times to avoid contamination of food with E. coli bacteria. This includes washing hands before and after handling food, cooking meat thoroughly to an internal temperature of at least 160°F (71°C), avoiding cross-contamination of raw and cooked foods, refrigerating leftovers promptly and discarding expired or spoiled foods .
• Water safety: Water safety measures should be taken to avoid drinking or using contaminated water for cooking or washing. This includes boiling water before use, using bottled water or water filters, avoiding ice cubes made from tap water and avoiding swallowing water when swimming in lakes, ponds or pools .
• Personal hygiene: Personal hygiene practices should be maintained to prevent the spread of E. coli bacteria from person to person. This includes washing hands frequently with soap and water, especially after using the toilet, changing diapers, handling animals or touching contaminated surfaces; avoiding sharing utensils, cups or towels with others; and staying home from work or school when sick .
• Travel precautions: Travel precautions should be taken when visiting areas where E. coli infection is common or where sanitation and hygiene standards are poor. This includes following the advice of "boil it, cook it, peel it or forget it" for food and water; avoiding street food vendors; choosing reputable restaurants; and taking prophylactic antibiotics if prescribed by a doctor .

E. coli food poisoning can be a serious illness that can cause severe complications in some cases. However, with proper treatment and prevention measures, most people can recover without any long-term consequences.

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