The eae Gene in Escherichia coli
The eae gene in E. coli encodes intimin, an outer membrane protein that is essential for the attaching and effacing (A/E) lesion formation characteristic of enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC) infections.
Function and Significance
The eae (Escherichia coli adherence element) gene is a critical virulence factor that plays several important roles:
Encodes intimin protein: The eae gene encodes intimin, an outer membrane adhesin protein that mediates intimate bacterial attachment to intestinal epithelial cells 1, 2
Mediates attaching and effacing lesions: Intimin is necessary for the formation of characteristic attaching and effacing (A/E) lesions on intestinal epithelial cells 3, 2
Diagnostic marker: The presence of eae is used to differentiate between bacterial pathotypes:
- EPEC is defined as eae-positive but stx-negative
- STEC (Shiga toxin-producing E. coli) is defined by the presence of Shiga toxin genes (stx1 and/or stx2) 1
Structural Characteristics
The eae gene has several notable structural features:
Polymorphic nature: Intimin is highly polymorphic, with at least 28 different alleles identified 4
Homology with invasin: The predicted amino acid sequence shares approximately 31% identity and 51% similarity with invasin of Yersinia pseudotuberculosis 2
Conserved and variable regions: The eae gene shows:
- High homology (97%) in the first 2200 bp between EPEC and EHEC strains
- Significant divergence (59% homology) in the last 800 bp at the C-terminus 3
Clinical Relevance
The eae gene has significant implications for pathogenesis and clinical outcomes:
Pathotype identification: The presence or absence of eae helps distinguish between different E. coli pathotypes that cause distinct clinical syndromes 1
Disease association: eae-positive strains are associated with:
- Diarrheal diseases
- Attaching and effacing lesions
- Potential for severe complications like hemolytic uremic syndrome (HUS) when combined with Shiga toxin genes 1
Diagnostic testing: Laboratory methods should detect both LEE-positive (containing eae) and LEE-negative STEC strains using culture, EIA, and PCR techniques 1
Evolutionary Significance
The eae gene shows interesting evolutionary characteristics:
Variant specificity: The C-terminal region of intimin, which shows the greatest divergence between EPEC and EHEC, is believed to be involved in receptor binding specificity 3, 2
Multiple subtypes: Fluorescent RFLP analysis has revealed at least 26 different fRFLP types corresponding to 20 of the 28 previously described eae alleles 4
Sequence variants: Multiple sequence variants have been identified for several alleles, including gamma, iota, kappa, zeta, and epsilon 4
The eae gene represents an important virulence determinant in pathogenic E. coli strains and serves as a crucial diagnostic marker for distinguishing between EPEC and STEC pathotypes, which has significant implications for patient management and public health interventions.