Enteropathogenic E. coli

Enteropathogenic Escherichia coli (EPEC) is a leading cause of acute and persistent diarrhea, particularly in infants and young children in low-resource settings. 

Characterized by its attaching and effacing (A/E) mechanism, EPEC disrupts the intestinal lining, leading to malabsorption and fluid loss. Early detection and supportive management are essential for reducing morbidity and complications.

What is Enteropathogenic E. coli?

Enteropathogenic Escherichia coli (EPEC) is a Gram-negative bacterial pathogen responsible for non-bloody, watery diarrhea. It primarily affects infants and young children, particularly in low-resource settings. 

Unlike other diarrheagenic E. coli, EPEC does not produce enterotoxins. Instead, it disrupts the intestinal lining through an attaching and effacing (A/E) mechanism, leading to malabsorption and fluid loss. 

Transmission occurs through contaminated food, water, and direct person-to-person contact.

Pathogenesis and Mechanism of Action

EPEC's pathogenicity is primarily driven by the Locus of Enterocyte Effacement (LEE), a chromosomal region that encodes key virulence proteins. These proteins facilitate bacterial attachment to intestinal cells and induce attaching and effacing (A/E) lesions, which disrupt the intestinal lining, impair nutrient absorption, and contribute to diarrhea.

EPEC colonizes the small intestine by adhering to epithelial cells using bundle-forming pili (BFP), which initiate localized attachment. It then injects virulence proteins through a Type III secretion system (T3SS), disrupting tight junctions, altering ion transport, and increasing gut permeability. 

The intimin protein (eae gene) facilitates firm attachment to enterocytes, while Esp proteins further inhibit chloride absorption, exacerbating fluid loss. 

Collectively, these mechanisms result in intestinal inflammation, malabsorption, and profuse diarrhea.

Clinical Presentation

EPEC infection typically presents with profuse, watery diarrhea, often accompanied by vomiting, dehydration, and low-grade or no fever. Unlike invasive bacterial pathogens, EPEC does not cause bloody diarrhea. 

In severe cases, especially in infants, prolonged diarrhea can lead to malnutrition and failure to thrive.

Atypical EPEC (aEPEC)  infections range from asymptomatic to severe diarrhea, with up to 40 BMs a day. aEPEC is commonly detected in both symptomatic and asymptomatic individuals, and adults with aEPEC infections are more likely to experience abdominal pain and prolonged diarrhea compared to children

Diagnostic Testing

The following tests are performed to determine the presence of E. coli:

Stool Culture

Stool cultures are performed on MacConkey agar, where EPEC appears as lactose-fermenting colonies. Biochemical identification includes indole positivity. However, stool culture alone cannot distinguish EPEC from other E. coli strains.

Molecular Testing (PCR)

PCR testing is the preferred diagnostic method due to its higher sensitivity and specificity. 

Molecular tests target:

• pEAF plasmid (confirms presence of typical EPEC).
• BFP gene (detects bundle-forming pili).
• eae gene (identifies attaching and effacing lesion-forming strains).

Multiplex PCR panels are increasingly used to rapidly detect EPEC alongside other diarrheagenic E. coli strains.

Test Interpretation

A stool culture test indicates a normal result by the absence of EPEC growth, while an EPEC-positive result is characterized by the presence of lactose-fermenting, indole-positive E. coli colonies. 

In addition, PCR testing for virulence markers (pEAF, BFP, eae) should be negative in a normal result, whereas detection of one or more of these virulence genes confirms an EPEC-positive outcome.

Typical EPEC (tEPEC): pEAF-positive.

Atypical EPEC (aEPEC): Lacks the pEAF plasmid but still carries the eae gene, making it more common in developed countries.

Management and Treatment

Management and treatment include:

Supportive Care (First-line Treatment)

• Oral Rehydration Therapy (ORT): Essential for preventing dehydration.
• Intravenous Fluids: Required for severe dehydration.
• Zinc Supplementation: Recommended in children to reduce diarrhea severity and duration.

Antibiotic Therapy (For Severe or Persistent Cases)

Antibiotics are not routinely recommended but may be considered for:

• Severe cases (e.g., prolonged diarrhea, dehydration).
• Immunocompromised patients.

Recommended antibiotic options include:

• Azithromycin (preferred in children).
• Ciprofloxacin (for adults in select cases).

Prevention Strategies

Preventing EPEC infections requires a combination of public health interventions:

• Hand hygiene with proper handwashing techniques.
• Safe drinking water through boiling or filtration.
• Improved sanitation to reduce fecal contamination.
• Breastfeeding to provide passive immunity in infants.

Clinical Relevance and Emerging Trends

EPEC continues to be a major cause of infantile diarrhea in developing nations, where limited sanitation and water access contribute to its prevalence. 

Meanwhile, atypical EPEC (aEPEC) is increasingly detected in both symptomatic and asymptomatic individuals in industrialized countries, suggesting a broader spectrum of disease presentation. 

From a public health perspective, early diagnosis and improved sanitation are critical for controlling EPEC transmission and reducing its burden on vulnerable populations.

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