Escherichia coli (E. coli) is a Gram-negative, rod-shaped bacterium that is commonly found in the intestines of humans and warm-blooded animals. It is a highly diverse species, comprising both harmless and pathogenic strains. The harmless strains are part of the normal gut flora and play a beneficial role in the digestive system by producing vitamin K2 and preventing the colonisation of pathogenic bacteria. However, certain strains of E. coli are pathogenic and can cause serious illness. These pathogenic strains can lead to various diseases, ranging from mild gastroenteritis to severe, life-threatening conditions such as hemolytic uremic syndrome (HUS). The diversity within the species makes E. coli a significant bacterium in both health and disease, necessitating ongoing research and public health efforts to manage and prevent infections.

Classification

E. coli, or Escherichia coli, is a well-studied bacterium classified within a hierarchical framework that reflects its evolutionary relationships and characteristics. The classification system used in microbiology places E. coli within specific taxonomic categories, each providing insight into its biology and ecology.

Kingdom: Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Unlike eukaryotes, bacterial cells do not contain a nucleus or other membrane-bound organelles. They are among the earliest forms of life on Earth and play crucial roles in ecosystems, including nutrient cycling, fermentation, and as pathogens.

Phylum: Proteobacteria

Proteobacteria is a major phylum of Gram-negative bacteria, which includes a wide variety of pathogens. Members of this phylum exhibit diverse shapes, metabolic pathways, and ecological roles. Proteobacteria are characterised by their double-membrane cell envelope.

Class: Gammaproteobacteria

Gammaproteobacteria is a class within the Proteobacteria phylum that includes many well-known bacteria, such as Salmonella, Vibrio, and Yersinia. This class encompasses a broad range of organisms, from free-living species to pathogens of humans, animals, and plants.

Order: Enterobacterales

Enterobacterales is an order within the Gammaproteobacteria class. Bacteria in this order are typically rod-shaped and Gram-negative. They are found in a variety of environments, including soil, water, and the intestines of animals. Many Enterobacterales are known for their medical and industrial significance.

Family: Enterobacteriaceae

Enterobacteriaceae is a large family of bacteria within the Enterobacterales order. Members of this family are facultatively anaerobic, meaning they can grow in both the presence and absence of oxygen. They are commonly found in the gastrointestinal tract of humans and animals. This family includes many important genera such as Escherichia, Salmonella, and Klebsiella.

Genus: Escherichia

The genus Escherichia is named after Theodor Escherich, a German bacteriologist who discovered E. coli. This genus is composed of facultatively anaerobic, rod-shaped bacteria that are commonly found in the intestines of warm-blooded organisms. Escherichia species play important roles in both health and disease.

Species: Escherichia coli (E. coli)

E. coli is the most well-known species within the Escherichia genus. It is a versatile bacterium that includes both harmless strains, which are part of the normal gut flora, and pathogenic strains, which can cause diseases such as gastroenteritis, urinary tract infections, and neonatal meningitis. E. coli has been extensively studied as a model organism in microbiology and biotechnology due to its relatively simple genetics and rapid growth.

The classification of E. coli highlights its placement within the broader context of bacterial diversity and its specific characteristics that differentiate it from other microorganisms. This hierarchical system aids scientists in studying its biology, ecology, and its interactions with hosts and environments.

Strains

E. coli encompasses a wide variety of strains, each with distinct characteristics and impacts on human health. These strains can be broadly categorised into non-pathogenic and pathogenic types.

Non-pathogenic Strains: Non-pathogenic strains of E. coli are typically harmless and are a natural part of the human gut flora. These strains play a crucial role in maintaining intestinal health by aiding in digestion, synthesising vitamins such as vitamin K and B12, and preventing the colonisation of harmful bacteria through competitive exclusion. These commensal E. coli strains are essential for a healthy digestive system and overall gut homeostasis.

Pathogenic Strains: Pathogenic strains of E. coli can cause various diseases and are responsible for a significant number of foodborne illnesses worldwide. Notable pathogenic strains include:

Enterotoxigenic E. coli (ETEC): ETEC is a leading cause of traveller’s diarrhoea and infant diarrhoea in developing countries. It produces two types of enterotoxins: heat-labile toxin (LT) and heat-stable toxin (ST), both of which cause the intestines to secrete excessive amounts of fluids and electrolytes. Infections typically occur through the consumption of contaminated food or water.

Enteropathogenic E. coli (EPEC): EPEC is a significant cause of diarrhoea in infants, especially in developing countries. This strain adheres to the intestinal epithelial cells and causes attaching and effacing (A/E) lesions, disrupting the microvilli and leading to malabsorption and diarrhoea. EPEC infections are often associated with poor sanitation and hygiene practices.

Enterohemorrhagic E. coli (EHEC): EHEC strains, including the notorious O157, can cause severe foodborne diseases. EHEC produces Shiga toxins, which in severe cases can lead to hemolytic uremic syndrome (HUS), a potentially life-threatening condition characterised by acute kidney failure, hemolytic anaemia, and thrombocytopenia. EHEC infections are often linked to undercooked ground beef, raw milk, and contaminated produce.

Enteroinvasive E. coli (EIEC): EIEC causes a disease similar to shigellosis, characterised by fever, cramps, and dysentery-like diarrhoea. EIEC invades and multiplies within the epithelial cells of the colon, causing significant inflammation and tissue destruction. The bacteria's ability to invade cells and evade the immune system is key to its pathogenicity.

Enteroaggregative E. coli (EAEC): EAEC is associated with persistent diarrhoea, particularly in children and immunocompromised individuals. This strain adheres to the intestinal mucosa in a distinctive stacked-brick pattern and produces toxins and other virulence factors that cause prolonged inflammation and damage to the intestinal lining. EAEC infections can lead to chronic diarrhoea and malnutrition in affected populations.

Understanding the different strains of E. coli and their mechanisms of pathogenicity is essential for developing targeted prevention and treatment strategies. Each strain's unique characteristics dictate its mode of transmission, the severity of the disease, and the most effective public health interventions to control its spread.

Pathogenesis

Pathogenic strains of E. coli have developed various sophisticated mechanisms to cause disease. These mechanisms enable the bacteria to colonise the host, evade the immune system, and damage host tissues, leading to a range of symptoms and illnesses.

Toxin Production: One of the primary mechanisms through which pathogenic E. coli strains cause disease is the production of toxins. Different strains produce different types of toxins, each with specific effects on the host. For example, Enterohemorrhagic E. coli (EHEC) produces Shiga toxins (Stx1 and Stx2), which inhibit protein synthesis in host cells. These toxins can cause severe damage to the intestinal lining, and, in serious cases, hemolytic uremic syndrome (HUS), a condition that can cause kidney failure. Enterotoxigenic E. coli (ETEC), on the other hand, produces heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST). LT stimulates the production of cyclic AMP (cAMP) in intestinal cells, leading to the secretion of water and electrolytes into the intestinal lumen. ST increases cyclic GMP (cGMP) levels in the intestinal cells, also causing fluid secretion and diarrhoea.

Adhesion: Pathogenic E. coli strains possess various adhesins, which are molecules that enable them to adhere to the surfaces of host cells. This adhesion is crucial for colonisation and infection. For instance, EHEC strains have intimin, a protein that mediates tight attachment to the intestinal epithelium. This close adherence disrupts the normal function of the intestinal cells and leads to the formation of attaching and effacing (A/E) lesions, which are characterised by the loss of microvilli and intimate attachment of the bacteria to the epithelial cell surface. Similarly, EPEC (Enteropathogenic E. coli) strains use a type III secretion system to inject effector proteins into host cells, facilitating strong adhesion and altering host cell function.

Invasion: Some E. coli strains can invade and multiply within host cells, a process that is crucial for their pathogenicity. Enteroinvasive E. coli (EIEC) strains are similar to Shigella in their ability to invade and replicate within the intestinal epithelial cells. They use a complex type III secretion system to deliver virulence factors that induce their uptake by host cells. Once inside, they escape from the phagocytic vacuole and replicate in the cytoplasm, leading to cell death and inflammation. This invasion disrupts the integrity of the intestinal epithelium, causing symptoms such as fever, cramping, and dysentery-like diarrhoea.

These mechanisms highlight the complex interactions between pathogenic E. coli strains and their hosts. By producing toxins, adhering to and invading host cells, these bacteria can cause a wide range of diseases, from mild gastrointestinal disturbances to severe, life-threatening conditions. Understanding these pathogenic mechanisms is crucial for developing effective treatments and preventive strategies against E. coli infections.

Symptoms and Diseases

Infections caused by pathogenic E. coli can manifest in a variety of symptoms and lead to several diseases, each with distinct clinical features and potential complications. Understanding these symptoms and the diseases they cause is crucial for timely diagnosis and appropriate treatment.

Gastroenteritis: One of the most common manifestations of E. coli infection is gastroenteritis, which involves inflammation of the stomach and intestines. The symptoms typically include diarrhoea, which can range from mild to severe. Other symptoms of gastroenteritis include abdominal pain, nausea, vomiting, and occasionally fever. The duration and severity of the symptoms depend on the specific strain of E. coli involved. For example, Enterotoxigenic E. coli (ETEC) often causes traveller’s diarrhoea, which is usually less severe but can still be highly disruptive.

Hemolytic Uremic Syndrome (HUS): Hemolytic uremic syndrome is a severe and potentially life-threatening complication that can arise from infection with Enterohemorrhagic E. coli (EHEC), particularly the O157 strain. HUS is characterised by the destruction of red blood cells (hemolysis), leading to anaemia, acute kidney failure, and a low platelet count (thrombocytopenia). Symptoms of HUS may include reduced urine output, fatigue, paleness, and easy bruising. The condition primarily affects young children and the elderly, requiring immediate medical intervention to prevent permanent kidney damage or other severe outcomes.

Urinary Tract Infections (UTIs): Uropathogenic E. coli (UPEC) is a major cause of urinary tract infections, which affect the bladder, urethra, and sometimes the kidneys. Symptoms of UTIs include a frequent and urgent need to urinate, a burning sensation during urination, cloudy or strong-smelling urine, and lower abdominal pain. If the infection spreads to the kidneys (pyelonephritis), additional symptoms such as fever, chills, and back pain may occur. UTIs are more common in women due to anatomical differences, but they can affect individuals of all ages and genders.

Neonatal Meningitis: Certain strains of E. coli can cause neonatal meningitis, a serious infection that leads to inflammation of the membranes surrounding the brain and spinal cord in newborns. This condition is typically caused by the K1 strain of E. coli. Symptoms in newborns may include fever, irritability, poor feeding, lethargy, and a bulging fontanel (the soft spot on a baby's head). Neonatal meningitis requires prompt medical treatment to prevent severe complications, including neurological damage and death.

In addition to these conditions, E. coli can also be implicated in other infections such as bloodstream infections (sepsis), which can occur when the bacteria enter the bloodstream from a primary site of infection. Sepsis caused by E. coli is a medical emergency and requires immediate treatment with antibiotics and supportive care.

Understanding the range of symptoms and diseases caused by E. coli infections is vital for healthcare providers to make accurate diagnoses and initiate appropriate treatments. Public awareness of these symptoms can also help individuals seek timely medical attention, reducing the risk of severe complications.

Transmission

E. coli is a bacterium that can be transmitted through various routes, primarily affecting the gastrointestinal system. Understanding the modes of transmission is essential for preventing infections and managing public health risks.

Faecal-Oral Route: The most common mode of transmission for E. coli is the faecal-oral route, which involves the consumption of food or water contaminated with faecal matter. This can occur when faeces from an infected person or animal contaminate food or water sources. Poor sanitation and inadequate hygiene practices can significantly increase the risk of transmission. For example, if contaminated water is used to irrigate crops or wash food products, the bacteria can easily be transferred to the food consumed by humans.

Person-to-Person Contact: E. coli can also spread through direct person-to-person contact, especially in environments where hygiene is compromised, such as in childcare centres, nursing homes, and other settings with close physical contact. In such environments, the bacterium can be transferred via contaminated hands after using the toilet or changing nappies, particularly if proper handwashing practices are not followed. Hand-to-mouth contact after touching contaminated surfaces can also facilitate the spread of E. coli.

Undercooked Meat: Consumption of undercooked meat, particularly ground beef, is a significant source of E. coli infection. Ground beef is especially prone to contamination because the process of grinding can spread the bacteria throughout the meat. Cooking meat to an internal temperature of at least 160°F (71°C) is essential to kill any E. coli present. Eating meat that has not been cooked thoroughly can result in the ingestion of live bacteria, leading to infection.

Raw Milk and Unpasteurised Dairy Products: E. coli can be present in raw milk and other unpasteurised dairy products, originating from the faeces of infected cows. Pasteurisation, which involves heating the milk to a high temperature for a short period, is an effective method to kill E. coli and other pathogens. Consumption of raw milk or dairy products made from raw milk carries a higher risk of infection and is discouraged by public health authorities.

Contaminated Produce: Vegetables and fruits can become contaminated with E. coli if they are exposed to contaminated water, either through irrigation or washing. Contamination can also occur during handling and processing if proper hygiene practices are not followed. Washing produce thoroughly under running water and, when possible, peeling or cooking it can reduce the risk of E. coli infection. Additionally, consumers are advised to avoid eating raw produce that has been recalled due to contamination concerns.

These transmission routes highlight the importance of maintaining good hygiene practices, ensuring proper food handling and preparation, and supporting public health measures to monitor and control E. coli contamination. Public education campaigns and regulatory measures are essential to minimise the risk of E. coli infections and protect public health.

Diagnosis

Diagnosing an E. coli infection involves several laboratory techniques to identify the presence and specific type of the bacterium causing the illness. Accurate diagnosis is essential for appropriate treatment and management of the infection.

Stool Culture: One of the primary methods for diagnosing E. coli infections is through stool culture. This process involves collecting a faecal sample from the patient and culturing it on selective media that promote the growth of E. coli while inhibiting other bacteria. The cultured bacteria are then subjected to various biochemical tests to confirm the presence of E. coli. Stool culture is particularly effective for detecting E. coli O157, a common pathogenic strain. However, it may not be as effective for identifying non-O157 serotypes, which require additional testing.

PCR (Polymerase Chain Reaction) and ELISA (Enzyme-Linked Immunosorbent Assay): Advanced molecular techniques like PCR and ELISA are used to detect specific genes or toxins associated with pathogenic E. coli strains. PCR is a highly sensitive method that amplifies DNA sequences unique to pathogenic E. coli, such as those encoding for Shiga toxins or virulence factors. This technique can provide rapid and accurate identification of pathogenic strains. ELISA, on the other hand, detects antigens or antibodies related to E. coli toxins. It is particularly useful for identifying toxins produced by EHEC strains. Both PCR and ELISA are valuable tools in confirming the presence of pathogenic E. coli, especially in cases where stool culture results are inconclusive.

Serotyping: Determining the specific strain of E. coli is crucial for understanding the epidemiology of an outbreak and tailoring appropriate public health responses. Serotyping involves identifying the unique antigens present on the surface of E. coli cells, specifically the O (somatic) and H (flagellar) antigens. This process helps distinguish between different serotypes of E. coli, such as E. coli O157 or E. coli O26. Serotyping is essential for tracing the source of infections and monitoring the spread of specific strains within populations. It also aids in identifying patterns of antibiotic resistance and virulence, which are critical for treatment and prevention strategies.

Combining these diagnostic methods provides a comprehensive approach to identifying E. coli infections. Stool cultures offer a reliable initial test, while PCR and ELISA provide detailed insights into the presence of specific pathogenic genes or toxins. Serotyping further refines the diagnosis by pinpointing the exact strain of E. coli involved. Accurate and timely diagnosis is vital for effective patient management, preventing the spread of infection, and implementing public health measures to control outbreaks.

Treatment

Treating E. coli infections involves various approaches depending on the severity and specific strain of the bacterium involved. The primary goals of treatment are to manage symptoms, prevent complications, and support the body’s recovery process.

Hydration: Maintaining adequate hydration is essential for managing diarrhoea and preventing dehydration, which is a common complication of E. coli infections. Patients are encouraged to drink plenty of fluids, such as water, oral rehydration solutions (ORS), and clear broths. ORS are particularly effective as they help replenish lost electrolytes and fluids, which are critical for maintaining bodily functions and preventing severe dehydration. In cases where oral intake is insufficient due to severe vomiting or diarrhoea, intravenous fluids may be administered to ensure proper hydration and electrolyte balance.

Antibiotics: The use of antibiotics in treating E. coli infections is a nuanced and sometimes controversial approach. For most E. coli strains, especially in mild cases, antibiotics are not recommended because the infection often resolves on its own. However, in severe cases or for specific strains, such as Enterotoxigenic E. coli (ETEC), antibiotics may be prescribed to shorten the duration of symptoms and reduce the severity of the illness. In contrast, for Enterohemorrhagic E. coli (EHEC) infections, antibiotics are typically avoided because they can increase the risk of complications. The use of antibiotics in EHEC can lead to the release of more Shiga toxins, exacerbating the condition and increasing the likelihood of developing hemolytic uremic syndrome (HUS), a serious complication that can cause kidney failure. Therefore, the decision to use antibiotics is carefully weighed by healthcare providers based on the specific strain and severity of the infection.

Supportive Care: Supportive care is a critical component of treating E. coli infections and focuses on alleviating symptoms and ensuring patient comfort. This includes encouraging rest to help the body fight the infection and recover. Maintaining electrolyte balance is crucial, especially in cases with significant fluid loss due to diarrhoea. Electrolyte supplements, either oral or intravenous, may be used to prevent imbalances that can affect heart and muscle function. Additionally, antidiarrheal medications are generally avoided as they can slow the elimination of the bacteria from the intestines, potentially prolonging the infection.

Overall, the treatment of E. coli infections requires a multifaceted approach tailored to the individual patient's needs and the specific characteristics of the infecting strain. Close monitoring and supportive care are often sufficient for mild cases, while severe infections may require more intensive interventions to prevent complications and support recovery.

Prevention

Preventing E. coli infections involves several key practices that focus on food safety, personal hygiene, and ensuring the cleanliness of water sources. These measures are crucial for minimising the risk of both individual and community-wide outbreaks.

Proper Food Handling: Ensuring that food is handled safely is paramount in preventing E. coli infections. This includes thoroughly cooking meat, particularly ground beef, to kill any bacteria that might be present. The recommended internal temperature for cooked meat is 160°F (71°C), which ensures that harmful bacteria are destroyed. Washing fruits and vegetables under running water helps remove potential contaminants from their surfaces. It's also essential to avoid cross-contamination by using separate cutting boards and utensils for raw meat and other foods, and by cleaning all surfaces and utensils thoroughly with soap and hot water after use. Additionally, refrigerating perishable items promptly can prevent bacterial growth.

Good Hygiene Practices: Maintaining good personal hygiene is another critical aspect of preventing E. coli transmission. Regular handwashing with soap and water, especially after using the toilet, changing diapers, and before preparing or eating food, significantly reduces the likelihood of spreading bacteria. Hands should be washed for at least 20 seconds, ensuring all parts of the hands, including under the nails and between fingers, are cleaned. In environments where soap and water are not available, using an alcohol-based hand sanitiser with at least 60% alcohol can be an effective alternative.

Safe Water Sources: Ensuring that water is clean and safe for consumption is vital in preventing E. coli infections, particularly in areas with limited access to clean water. Drinking water should be sourced from safe, treated supplies. In situations where the safety of the water supply is uncertain, boiling water for at least one minute can kill harmful bacteria and other pathogens. Additionally, using water filters certified to remove bacteria or treating water with disinfectants like chlorine can also ensure its safety. It's also important to avoid swallowing water from lakes, rivers, or swimming pools that may be contaminated.

These preventive measures are essential for reducing the risk of E. coli infections. By adhering to proper food handling techniques, maintaining rigorous hygiene practices, and ensuring the safety of water sources, individuals can significantly lower the chances of contracting and spreading E. coli. Public health education and awareness campaigns play a crucial role in disseminating this information and encouraging the adoption of these practices at both individual and community levels.

Research and Public Health

E. coli remains a significant focus of research and public health efforts due to its impact on food safety and its role as a model organism in molecular biology. This bacterium's influence on food safety is profound because pathogenic strains can cause severe outbreaks, leading to illness and even death. Researchers are continuously exploring the mechanisms by which E. coli causes disease, aiming to understand the specific factors that make certain strains pathogenic. This involves studying the bacteria's ability to produce toxins, adhere to and invade host tissues, and evade the immune system.

Another crucial area of research is the bacterium's resistance to antibiotics. The rise of antibiotic-resistant E. coli strains poses a serious threat to public health, making it essential to investigate how these bacteria acquire resistance and to develop new strategies for combatting infections. This includes studying genetic mutations and horizontal gene transfer that contribute to resistance, as well as exploring alternative treatments such as bacteriophage therapy and novel antimicrobial agents.

In addition to its pathogenic aspects, E. coli is a key model organism in molecular biology. Its relatively simple genome and the availability of various genetic tools make it an ideal subject for studying fundamental biological processes. Research using E. coli has led to significant advancements in understanding DNA replication, transcription, translation, and genetic regulation. These studies have broad implications, informing research on more complex organisms and contributing to the development of biotechnological applications, such as the production of recombinant proteins and biofuels.

Public health efforts are closely tied to these research initiatives. Surveillance programs monitor E. coli infections to detect and respond to outbreaks swiftly. Public health campaigns emphasise the importance of proper food handling, hygiene, and cooking practices to prevent infection. Additionally, guidelines and regulations are continually updated based on the latest research findings to improve food safety and reduce the incidence of E. coli-related illnesses.

Overall, the combined efforts of researchers and public health professionals aim to mitigate the impact of E. coli on human health, enhance our understanding of bacterial biology, and develop effective strategies to prevent and treat infections.

Major E. coli Outbreaks in the UK

Central Scotland Outbreak (1996)

Strain: E. coli O157

Source: Contaminated cooked meat from a butcher shop in Wishaw, Scotland.

Impact: 21 deaths and over 400 cases of illness.

Response: The outbreak led to increased scrutiny on food safety practices and improvements in food hygiene regulations.

South Wales Outbreak (2005)

Strain: E. coli O157

Source: Contaminated meat supplied to schools by a local butcher.

Impact: 1 child died, and over 150 people, mostly schoolchildren, were affected.

Response: Resulted in a major public inquiry, which led to recommendations for stricter food safety standards and better enforcement.

Godstone Farm Outbreak (2009)

Strain: E. coli O157

Source: Contact with animals at Godstone Farm in Surrey.

Impact: 93 confirmed cases, mainly affecting children.

Response: The incident highlighted the risks of petting farms and led to improved guidelines for managing public health risks at such facilities.

Redhill Outbreak (2012)

Strain: E. coli O157

Source: Raw milk from a dairy farm in Redhill, Surrey.

Impact: 5 confirmed cases.

Response: This outbreak resulted in heightened surveillance and stricter regulations on raw milk sales.

Multi-Country Outbreak Linked to Salad Leaves (2016)

Strain: E. coli O157

Source: Mixed salad leaves imported from the Mediterranean region.

Impact: 161 confirmed cases in the UK, with 2 deaths.

Response: Emphasised the need for improved traceability and safety standards in the supply chain of fresh produce.

Preston Outbreak (2017)

Strain: E. coli O157

Source: Unknown, but linked to a local food establishment.

Impact: Over 20 cases reported.

Response: Led to temporary closure of the establishment and an investigation into food handling practices.

Ongoing Surveillance and Response

The UK has established robust surveillance systems to monitor E. coli infections and prevent outbreaks. Key measures include:

Enhanced Food Safety Regulations: Regular updates to food safety laws and guidelines to ensure best practices are followed in food production, processing, and handling.

Public Health Campaigns: Efforts to educate the public and food industry workers about hygiene practices, such as proper handwashing, cooking meats thoroughly, and avoiding cross-contamination.

Rapid Response Protocols: Quick identification and response to outbreaks through the coordination of health agencies, including Public Health England (now integrated into the UK Health Security Agency) and the Food Standards Agency (FSA).

Research and Monitoring: Ongoing research into the sources and transmission pathways of E. coli, as well as the development of new technologies for detection and prevention.

2024 UK E. coli Outbreak

As of June 2024, the UK is experiencing a significant E. coli outbreak, with over 211 confirmed cases of Shiga toxin-producing E. coli (STEC) O145 reported since May 25th. The outbreak has been linked to a nationally distributed food item, although the exact source has not yet been identified​. (1, 2)

Affected Regions: The majority of the cases have been reported in England, with additional cases in Wales, Scotland, and Northern Ireland​.

Age Range: The affected individuals range from 2 to 79 years old, with a significant number of cases occurring among young adults​.

Hospitalisations: Approximately 67 people have been hospitalised due to the severity of the infection​​.

STEC infections can cause severe symptoms, including diarrhoea, stomach cramps, and vomiting. In severe cases, particularly among children, the infection can lead to hemolytic uremic syndrome (HUS), a potentially life-threatening condition that causes kidney failure​.

The UK Health Security Agency (UKHSA) is collaborating with other public health bodies, including the Food Standards Agency (FSA) and Food Standards Scotland, to trace the source of the outbreak. They have advised the public to practice good hygiene, such as thorough hand washing, especially after using the toilet and before preparing food​.

Further investigations, including whole genome sequencing of samples, are ongoing to identify the contaminated food item(s). Public health officials expect the number of confirmed cases to rise as more data becomes available​.

Summary

E. coli is a remarkably versatile bacterium that encompasses both harmless and harmful strains. The non-pathogenic strains of E. coli are a natural and essential part of the normal gut flora in humans and animals. These strains contribute to the healthy functioning of the digestive system, aiding in the synthesis of vital vitamins such as vitamin K and preventing colonisation by pathogenic bacteria through competitive exclusion. However, certain strains of E. coli are pathogenic and can cause a range of illnesses. These illnesses can vary widely in severity, from mild gastrointestinal disturbances like diarrhoea to severe, life-threatening conditions such as hemolytic uremic syndrome (HUS), which can lead to kidney failure.

Pathogenic strains of E. coli, such as E. coli O157, produce toxins and possess other virulence factors that enable them to cause disease. These strains can enter the body through contaminated food or water, direct contact with infected animals or persons, or exposure to environments contaminated with faecal matter. Once inside the host, pathogenic E. coli can adhere to the intestinal lining, produce harmful toxins, and induce inflammatory responses that lead to symptoms ranging from mild to severe.

Understanding the different strains of E. coli is crucial for both prevention and treatment. Each strain has unique characteristics that influence its mode of transmission, virulence, and the specific illnesses it can cause. Research into these strains helps in developing targeted public health strategies, such as improved food safety protocols and better hygiene practices, to prevent outbreaks. Additionally, recognising the symptoms associated with different pathogenic strains aids in prompt diagnosis and effective treatment, reducing the risk of severe complications.

Preventive measures play a key role in controlling the spread of E. coli-related diseases. These measures include proper food handling and cooking practices, regular handwashing, especially after using the bathroom or handling raw food, and ensuring clean water supply. Public health initiatives also focus on educating the public about the risks associated with E. coli and the importance of maintaining good hygiene practices.

In summary, a comprehensive understanding of E. coli's various strains, their transmission modes, and effective preventive measures is essential for managing and controlling the diseases caused by this versatile bacterium. This knowledge helps in mitigating the health risks posed by pathogenic strains and ensures the continued benefits provided by the harmless strains within the gut flora.