The commonly-used DNA probe for diffusely-adherent <it>Escherichia coli </it>cross-reacts with a subset of enteroaggregative <it>E. coli</it>

<p>Abstract</p> <p>Background</p> <p>The roles of diffusely-adherent <it>Escherichia coli </it>(DAEC) and enteroaggregative <it>E. coli </it>(EAEC) in disease are not well understood, in part because of the limitations of diagnostic tests for each of these categories of diarrhoea-causing <it>E. coli</it>. A HEp-2 adherence assay is the Gold Standard for detecting both EAEC and DAEC but DNA probes with limited sensitivity are also employed.</p> <p>Results</p> <p>We demonstrate that the <it>daaC </it>probe, conventionally used to detect DAEC, cross-reacts with a subset of strains belonging to the EAEC category. The cross hybridization is due to 84% identity, at the nucleotide level, between the <it>daaC </it>locus and the aggregative adherence fimbriae II cluster gene, <it>aafC</it>, present in some EAEC strains. Because <it>aaf</it>-positive EAEC show a better association with diarrhoea than other EAEC, this specific cross-hybridization may have contributed to an over-estimation of the association of <it>daaC </it>with disease in some studies. We have developed a discriminatory PCR-RFLP protocol to delineate EAEC strains detected by the <it>daaC </it>probe in molecular epidemiological studies.</p> <p>Conclusions</p> <p>A PCR-RFLP protocol described herein can be used to identify <it>aaf</it>-positive EAEC and <it>daaC</it>-positive DAEC and to delineate these two types of diarrhoeagenic <it>E. coli</it>, which both react with the <it>daaC </it>probe. This should help to improve current understanding and future investigations of DAEC and EAEC epidemiology.</p>

Abstract licence: CC BY-NC-ND

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