Abstract
Enteroaggregative Escherichia coli (EAEC) has been implicated in sporadic diarrhea in children and adults and has been identified as the cause of several outbreaks worldwide. The HEp-2 test remains the gold standard for identification of this pathotype. A 60-65 MDa plasmid encodes the aggregative adherence fimbriae (AAF/I and AAF/II), a transcriptional activator (aggR gene), the enteroaggregative heat-stable enterotoxin EAST1 (astA gene) and a cytotoxin (Pet). The standard assay for EAEC is performed only in research laboratories, because it is expensive, labor intensive and time-consuming. The Polymerase Chain Reaction (PCR) offers the possibility of rapid diagnosis. In the current study, a multiplex PCR assay which checks aggR and astA genes was designed. Eigthy-eight E. coli strains, isolated from children with acute diarrhea in Mendoza, Argentina, were characterized by the reference method (HEp-2 assay), and by aggR-astA PCR. A strong correlation between the presence of the specific marker aggR and the reference test was found. The astA gene had a similar distribution between aggregative and localized strains, indicating that this gene could not be considered as a marker of EAEC. We conclude that aggR may be used to identify EAEC, using the PCR method as a screening test.
Highlights
Epidemiological studies done in the past century have demonstrated an association of specific serotypes of Escherichia coli and diarrhea
Strains belonging to these serotypes were referred as Enteropathogenic Escherichia coli (EPEC), but early studies did not identify any pathogenic factor, that could account for their pathogenicity
This test allows to differenciate among all three adherent diarrheigenic categories: EPEC, Diffuse Adherence Escherichia coli (DAEC) and Enteroaggregative Escherichia coli (EAEC)
Summary
Epidemiological studies done in the past century have demonstrated an association of specific serotypes of Escherichia coli and diarrhea. With the HEp-2 or Hela cell assay three distinct patterns of adherence have been described: Localized Adherence (LA) in which bacteria form characteristic microcolonies on the surface of the HEp-2 cell (Fig. 1), Diffuse Adherence (DA), in which bacteria adhere evenly to the whole cell surface (Fig. 2), and aggregative adherence, in which aggregated bacteria attach to the cell in a stacked-brick arrangement (Fig. 3). This test allows to differenciate among all three adherent diarrheigenic categories: EPEC, Diffuse Adherence Escherichia coli (DAEC) and Enteroaggregative Escherichia coli (EAEC)
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