Enteroaggregative Escherichia coli (EAEC) is a type of E. coli that causes diarrheal illness. Unlike Shiga toxin-producing E. coli (STEC), which often causes severe, bloody diarrhea, EAEC is known for both acute and persistent diarrheal episodes worldwide.
Understanding Enteroaggregative E. coli
EAEC is characterized by its “aggregative adherence” pattern, where the bacteria clump together and stick to intestinal cells in a distinctive “stacked-brick” formation. This adherence is mediated by structures called aggregative adherence fimbriae (AAF), which are filamentous proteins that allow the bacteria to bind to host tissues. This adherence enables EAEC to form a thick, aggregating biofilm on the intestinal lining, primarily in the colon and sometimes the small intestine. The biofilm helps the bacteria evade the host’s immune system and contributes to persistent infection.
Following colonization, EAEC produces toxins, including heat-stable enterotoxin 1 (EAST1) and Shigella enterotoxin 1 (ShET1), which contribute to intestinal secretion and inflammation. Another factor is dispersin, a secreted protein that helps with bacterial dispersion. The aggregative regulator (AggR) is a transcriptional factor that controls the expression of many virulence factors, including those involved in fimbriae biogenesis and toxin production.
Symptoms and Illness
Individuals infected with EAEC commonly experience watery diarrhea, which can sometimes contain mucus. This is often accompanied by abdominal pain or cramps, nausea, and vomiting. A low-grade fever may also be present.
Symptoms typically begin 8 to 48 hours after exposure. While many infections are self-limiting, EAEC diarrhea is known for its potential to be prolonged or persistent, sometimes lasting over 14 days, especially in children. The duration of illness commonly ranges from 3 to 4 days, though some individuals may experience symptoms for 2 weeks or longer. Symptom variation can be influenced by factors such as the host’s immune response, the specific EAEC strain, and the amount of bacteria ingested.
Transmission and Prevention
EAEC spreads primarily through the fecal-oral route, meaning the bacteria are transmitted when microscopic amounts of infected feces are ingested. Common sources of infection include consuming contaminated food and water, such as raw or undercooked meats, unwashed fruits or vegetables, or untreated water and unpasteurized milk.
Direct person-to-person contact is another way EAEC can spread, particularly when individuals do not wash their hands properly after using the bathroom or caring for an infected person. Contaminated surfaces and objects can also facilitate transmission. EAEC is a frequent cause of “traveler’s diarrhea” but can be acquired anywhere.
Preventive measures focus on breaking the chain of transmission. Hand hygiene is essential, especially after using the bathroom, changing diapers, or handling raw meat or animals.
Safe food preparation practices include cooking all meats thoroughly and preventing cross-contamination between raw and cooked foods by using separate utensils and cutting boards. Washing fruits and vegetables before consumption is also important. Drinking safe water, avoiding untreated water, and choosing pasteurized milk and juices further reduce the risk of infection. When traveling, extra precautions with food and water are advisable.
Diagnosis and Treatment Approaches
Diagnosing EAEC infections typically involves laboratory analysis of stool samples. While traditional stool cultures can be used, identifying EAEC based on its characteristic aggregative adherence to HEp-2 cells in culture can be a cumbersome process. More specific molecular tests, such as polymerase chain reaction (PCR), can detect EAEC bacterial DNA in stool samples, offering a more rapid and sensitive method for identification. However, the genetic heterogeneity among EAEC strains can make it challenging to identify a single virulence factor common to all strains for diagnostic purposes.
Treatment for EAEC infections primarily focuses on supportive care, with rehydration therapy as the cornerstone. Oral rehydration solutions (ORS) are recommended to replace fluids and electrolytes lost due to diarrhea, and even small, frequent sips can be beneficial, especially for young children. Intravenous hydration may be necessary in cases of severe dehydration.
Antibiotics are generally not routinely recommended for EAEC infections due to concerns about antibiotic resistance and the self-limiting nature of most cases. However, they may be considered in specific situations, such as severe or persistent illness, in immunocompromised individuals, or when guided by specific clinical guidelines. Azithromycin and rifaximin are examples of antibiotics that have been shown to shorten the course of EAEC diarrhea in adults and may be recommended for severe or persistent cases in children. Anti-motility agents are generally not advised for diarrheal illnesses with fever or bloody stools.
Potential Complications
Complications from EAEC infections can arise, particularly in vulnerable populations. The most significant concern is severe dehydration due to fluid and electrolyte loss from prolonged diarrhea and vomiting. This can lead to serious health issues and may necessitate hospitalization.
Persistent diarrhea caused by EAEC, especially in young children, can contribute to malnutrition and growth faltering. This occurs because the ongoing intestinal illness can impair the absorption of nutrients necessary for healthy development. Children who are already undernourished may experience intensified EAEC infections and worse growth outcomes. In some instances, EAEC has been linked to the development of post-infectious irritable bowel syndrome, although more research is needed to confirm this association.