IS3 profiling identifies the enterohaemorrhagic Escherichia coli O-island 62 in a distinct enteroaggregative E. coli lineage

To identify genetic loci conserved within significant EAEC lineages, but absent from non-EAEC, IS3-based PCR profiles were generated for 22 well-characterised EAEC strains. Six bands that were conserved among, or missing from, specific EAEC lineages were cloned and sequenced. One band corresponded to the aggR gene, a plasmid-encoded regulator that has been used as a diagnostic target but predominantly detects EAEC bearing the plasmid already marked by CVD432. The sequence from a second band was homologous to an open-reading frame within the cryptic enterohaemorrhagic E. coli (EHEC) O157 genomic island, designated O-island 62. Screening of an additional 46 EAEC strains revealed that the EHEC O-island 62 was only present in those EAEC strains belonging to the ECOR phylogenetic group D, largely comprised of sequence type (ST) complexes 31, 38 and 394.The EAEC 042 gene orf1600, which lies within the EAEC equivalent of O-island 62 island, can be used as a marker for EAEC strains belonging to the ECOR phylogenetic group D. The discovery of EHEC O-island 62 in EAEC validates the genetic profiling approach for identifying conserved loci among phylogenetically related strains.Enteroaggregative Escherichia coli (EAEC) were originally associated with persistent diarrhoea in developing countries but are now known to cause both acute and persistent diarrhoea worldwide [1]. EAEC strains all demonstrate a characteristic aggregative adherence to human epithelial cells in vivo or in culture. There are no other phenotypic or genotypic properties known to be shared by all EAEC strains, and the contribution of potential EAEC virulence factors to human disease is yet to be assessed. Volunteer studies and outbreaks have unequivocally demonstrated that at least some EAEC strains are pathogens [2-5]. However, epidemiological studies have always recovered EAEC from healthy people as well as individuals with diarrhoea. Although host factors are one reason for this observation [6,7], it is al