What is Enteroaggregative E. coli (EAEC)?
Enteroaggregative Escherichia coli (EAEC) is one of six diarrheagenic E. coli pathotypes that causes acute or persistent watery diarrhea worldwide, characterized by its distinctive "stacked-brick" or "aggregative adherence" pattern when bacteria adhere to intestinal epithelial cells 1, 2.
Key Defining Characteristics
EAEC is defined by several critical features that distinguish it from other pathogenic E. coli:
- Adherence Pattern: The hallmark is aggregative adherence (AA) - bacteria attach to epithelial cells in a characteristic stacked-brick arrangement, which was historically the gold standard for clinical identification 1, 3
- Strong Biofilm Formation: EAEC strains produce robust biofilms on both epithelial cells and abiotic surfaces 1
- Heterogeneous Nature: Not all EAEC strains cause disease; they vary significantly in virulence factors and pathogenic potential 2
Clinical Presentation
EAEC causes:
- Watery diarrhea (with or without mucus) that can be acute or persistent 2
- Predominantly affects children in low-income countries 2
- Traveler's diarrhea in both children and adults in middle and high-income countries 2
- Mucosal inflammation in infected individuals 4
- Can occasionally be life-threatening in vulnerable patients when strains possess additional virulence determinants 2
Pathogenesis Mechanism
The disease process involves three main steps 4:
- Colonization of the intestinal mucosa
- Elaboration of enterotoxins and cytotoxins
- Induction of mucosal inflammation
Virulence Factors
EAEC virulence is controlled by a master regulator called AggR, which defines "typical EAEC" strains 4, 5:
- Aggregative adherence fimbriae (AAF): Five types (AAF/I through AAF/V) mediate attachment 1, 6
- SPATEs: Serine protease autotransporters of Enterobacteriaceae 1
- Dispersin protein: Facilitates bacterial spread 5
- Type VI secretion system: Additional virulence mechanism 5
These factors are encoded on the plasmid of aggregative adherence (pAA) or chromosomal pathogenicity islands 2.
Molecular Identification
Modern diagnosis has shifted from phenotypic to molecular methods 1:
- PCR detection of genes like aggA, agg3A, agg4A, agg5A, aafA, afpA, and aggR 6
- DNA sequencing techniques 1
- The variability in plasmid structure necessitates including chromosomal markers in screening assays 2
Important Clinical Considerations
Multidrug resistance is common and geographically widespread in EAEC 2, which has significant implications for treatment decisions. The 2017 IDSA guidelines do not specifically list EAEC in their clinical presentations table 7, reflecting that it typically causes watery rather than bloody diarrhea and may not require specific identification in routine clinical practice unless persistent or in outbreak settings.
Whole-genome sequencing has revealed that horizontal gene transfer and recombination drive acquisition of novel virulence mechanisms 2, meaning EAEC continues to evolve as a public health threat.