Escherichia coli is a common bacterium, with most strains residing harmlessly in the human gut. Some strains, however, are pathogenic and cause illness. Enteroaggregative E. coli (EAEC) is one such strain, recognized globally as a significant cause of both acute and chronic diarrhea. It is distinct from other diarrheal E. coli strains due to its unique mechanism of colonizing the intestinal lining. Understanding EAEC involves examining how it adheres to the gut, how it spreads, and how the resulting infection is managed.
Unique Characteristics of EAEC
EAEC distinguishes itself through its signature method of attaching to the intestinal wall, characterized by a clumping behavior. Under a microscope, the bacteria adhere to host cells in a characteristic “stacked-brick” pattern. This adherence is mediated by specialized, hair-like appendages called aggregative adherence fimbriae (AAF).
The AAF structures enable the bacteria to stick to each other and to the intestinal epithelial cells, facilitating the creation of a thick, protective biofilm. Biofilm formation is central to EAEC’s ability to cause persistent infection, as the aggregated bacteria are shielded from the body’s natural defenses and the flow of gut contents. The production of these adherence factors is controlled by the AggR master regulator.
Once attached, EAEC strains release toxins that contribute to illness symptoms. These include the Enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1) and the plasmid-encoded toxin (Pet). These toxins disrupt normal fluid absorption and cause inflammation in the intestine. The result is the persistent secretion of fluid into the gut lumen, leading to characteristic watery diarrhea.
Transmission and Global Impact
EAEC is transmitted through the fecal-oral route, meaning the bacteria are ingested via food or water contaminated with human or animal feces. It is a major concern in areas with inadequate sanitation and limited access to safe drinking water. Common sources of infection include contaminated produce, unpasteurized dairy, and poorly handled street food.
The bacterium has a significant global presence and is a major cause of infectious diarrhea in travelers, often ranking second only to enterotoxigenic E. coli. EAEC is isolated in a substantial percentage of traveler’s diarrhea cases, highlighting its ubiquity in high-risk regions.
EAEC infection poses a particular risk to vulnerable populations, including infants, young children, and immunocompromised individuals. In young children in developing countries, persistent EAEC infection is linked to long-term health issues beyond acute illness. These chronic infections can contribute to malnutrition, growth stunting, and impaired cognitive development.
Symptoms and Treatment Strategies
The clinical presentation of EAEC infection typically involves the sudden onset of watery diarrhea, which may contain mucus. Patients often experience abdominal cramps, a low-grade fever, and general malaise. A distinguishing feature of EAEC is its tendency to cause diarrhea that persists for more than 14 days, particularly in children and immunocompromised adults.
Diagnosis is often performed using specialized molecular tests, such as PCR-based assays, to detect specific virulence genes like the AggR regulon. However, specific testing is not always pursued, as mild infections are generally self-limiting.
The primary management strategy is supportive care, focusing on preventing or correcting dehydration. Oral rehydration therapy (ORT)—consuming fluids with the correct balance of water, salts, and sugar—is the standard of care for replacing lost electrolytes and preventing complications, especially in young children.
Antibiotics are not routinely recommended, as most infections resolve on their own. They may be considered, however, for severe or persistent diarrhea, or for patients with compromised immune systems. Medications such as ciprofloxacin, azithromycin, or rifaximin can shorten the duration of illness in certain patient groups, particularly travelers. Prevention involves rigorous personal hygiene, such as frequent hand washing, and adhering to food safety guidelines when traveling in high-risk areas.