Enteroaggregative E. coli (EAEC)

Pathogenic Mechanisms of Enteroaggregative E. coli (EAEC)

Enteroaggregative E. coli (EAEC) leads to disease through its ability to adhere to intestinal cells and produce toxins which trigger inflammation. The initial step of bacterial infection starts when E. coli adheres to intestinal epithelial cells through fimbrial and afimbrial adhesins. The bacteria create the distinctive "aggregative adherence" (AA) pattern through adhesion which enables them to form biofilms that protect them from the immune system and antibacterial agents. Biofilms develop with excessive mucus production and typically appear in the colon and small intestine. The toxins Pet and EAST-1 and ShET1 and Pic produced by established EAEC infections lead to microvillus vesiculation and enlarged crypt openings and increased epithelial cell extrusion. The toxins produced by EAEC lead to secretory diarrhea which represents the primary symptom of this bacterial infection. The host immune system produces an intense inflammatory reaction when infected by EAEC through innate immunity mechanisms that are influenced by bacterial virulence factors. The presence of elevated fecal cytokines and inflammatory markers including IL-1β, IL-8, IFN-γ, lactoferrin and leukocytes has been documented in patients with EAEC infections. The flagellin protein FliC from EAEC bacteria can stimulate IL-8 production in host cells but genetic variations in the CD14 promoter region determine how well individuals can fight off EAEC diarrhea. The pathogenic mechanisms of EAEC depend on its ability to adhere to surfaces and produce toxins and trigger inflammatory responses.

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Figure 2. The 3-steps model of EAEC pathogenesis. (Van Nederveen, 2025)

EAEC Diagnostic Approaches

The current gold standard for detecting enteroaggregative Escherichia coli (EAEC) involves showing the aggregative adherence (AA) pattern on HeLa or HEp-2 cells. The phenotypic test for AA pattern identification on HeLa or HEp-2 cells remains the gold standard but it is time-consuming and expensive and needs specialized laboratory equipment which restricts its application in routine testing. The development of molecular diagnostic methods has been necessary to address these testing challenges. The CVD432 DNA probe, originally derived from a cryptic fragment of the pAA1 plasmid in EAEC strain 17-2, was the first widely used molecular tool. It was later identified as part of the aatA gene within the dispersin-secretion system operon. The aatA (or AA) probe demonstrates high specificity but variable sensitivity (20–89%) compared to the AA pattern, and its plasmid-borne nature limits detection of atypical EAEC strains. Multiplex PCR assays have been designed for simultaneous detection of all diarrheagenic E. coli pathotypes, but EAEC detection typically relies on only one or two pAA markers, again excluding atypical strains. Recent advances suggest that combining detection of plasmid and chromosomal markers improves diagnostic coverage. The detection of typical and atypical EAEC subgroups becomes possible through assays that target the aatA, aggR and aaiG/aaiC genes. The molecular detection methods enable quick and accessible testing with high precision which makes them essential for both research investigations and medical diagnostic applications.