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Open Access Methodology article

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

Anna M Snelling1, Louissa R Macfarlane-Smith1, Jonathan N Fletcher1 and Iruka N Okeke12*

Author affiliations

1 Division of Biomedical Sciences and Bradford Infection Group, University of Bradford, Bradford, West Yorkshire, BD7 1DP, UK

2 Department of Biology, Haverford College, 370 Lancaster Avenue, Haverford, PA 19041, USA

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Citation and License

BMC Microbiology 2009, 9:269  doi:10.1186/1471-2180-9-269

Published: 21 December 2009

Abstract

Background

The roles of diffusely-adherent Escherichia coli (DAEC) and enteroaggregative E. coli (EAEC) in disease are not well understood, in part because of the limitations of diagnostic tests for each of these categories of diarrhoea-causing E. coli. A HEp-2 adherence assay is the Gold Standard for detecting both EAEC and DAEC but DNA probes with limited sensitivity are also employed.

Results

We demonstrate that the daaC 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 daaC locus and the aggregative adherence fimbriae II cluster gene, aafC, present in some EAEC strains. Because aaf-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 daaC with disease in some studies. We have developed a discriminatory PCR-RFLP protocol to delineate EAEC strains detected by the daaC probe in molecular epidemiological studies.

Conclusions

A PCR-RFLP protocol described herein can be used to identify aaf-positive EAEC and daaC-positive DAEC and to delineate these two types of diarrhoeagenic E. coli, which both react with the daaC probe. This should help to improve current understanding and future investigations of DAEC and EAEC epidemiology.