eae-negative attaching and effacing Escherichia coli from piglets with diarrhea

Area of Science:

• Veterinary Microbiology
• Bacteriology
• Molecular Biology

Background:

• Escherichia coli (E. coli) is a significant pathogen in swine.
• Certain E. coli strains cause attaching and effacing (A/E) lesions, contributing to enteric disease.
• The eae gene, encoding intimin, is typically associated with A/E lesion formation.

Purpose of the Study:

• To investigate the characteristics of enterotoxin- and cytotoxin-negative E. coli strains isolated from diarrheic pigs.
• To determine the prevalence of A/E lesion-inducing capabilities and the presence of the eae gene in these isolates.
• To evaluate the utility of phenotypic assays versus genetic detection for identifying A/E E. coli.

Main Methods:

• Isolation and characterization of 190 E. coli strains from diarrheic pigs in São Paulo, Brazil.
• Adherence assays using HeLa cells and HEp-2 cells.
• Fluorescence actin staining (FAS) for detecting actin rearrangement.
• Transmission electron microscopy (TEM) for visualizing A/E lesions.
• Polymerase chain reaction (PCR) for eae gene detection.
• Western blot for intimin production and serogrouping.

Main Results:

• Forty-seven of 190 isolates adhered to HeLa cells, but not in a localized pattern.
• Seven of the adherent strains showed positive, though often weak or atypical, fluorescence actin staining (FAS).
• Four strains (one FAS-negative, three FAS-positive) induced A/E lesions on HEp-2 cells, yet all lacked the eae gene.
• Intimin production was detected in some strains, and serogrouping was performed.

Conclusions:

• A subset of E. coli strains from diarrheic pigs can induce A/E lesions independently of the eae gene.
• Phenotypic methods like FAS and lesion observation may be more sensitive for detecting certain A/E E. coli than PCR-based gene detection alone.
• Relying solely on eae gene detection might underestimate the prevalence of A/E pathogenic E. coli in swine.