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ABSTRACTAdherent-invasive Escherichia coli(AIEC) pathovar strains, which are associated with Crohn's disease, share many genetic and phenotypic features with extraintestinal pathogenic E. coli(ExPEC) strains, but little is known about the level of genetic similarity between the two pathovars. We aimed to determine the frequency of strains with the “AIEC phenotype” among a collection of ExPEC strains and to further search for a common phylogenetic origin for the intestinal and extraintestinal AIEC strains. The adhesion, invasion, and intramacrophage replication capabilities (AIEC phenotype) of 63 ExPEC strains were determined. Correlations between virulence genotype and AIEC phenotype and between intestinal/extraintestinal origin, serotype, and phylogroup were evaluated for the 63 ExPEC and 23 intestinal AIEC strains. Phylogenetic relationships between extraintestinal and intestinal AIEC strains were determined using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis. Only four (6.35%) ExPEC strains, belonging to the O6:H1, O83:H1, and O25:H4 serotypes, were classified as having an AIEC phenotype. These strains were found to be genetically related to some intestinal AIEC strains of the same serotypes as revealed by MLST. No particular virulence gene sets correlated with the intestinal/extraintestinal origin of the strains or with the AIEC phenotype, whereas the gene sets did correlate with the serogroup. We identified two intestinal AIEC strains and one extraintestinal AIEC strain belonging to the O25:H4 serotype that also belonged to the emerging and virulent clonal group ST131. In conclusion, the ExPEC and AIEC pathovars share similar virulence gene sets, and certain strains are phylogenetically related. However, the majority of ExPEC strains did not behave like AIEC strains, thus confirming that the AIEC pathovar possesses virulence-specific features that, to date, are detectable only phenotypically.

ABSTRACTLpf (stands for long polar fimbriae) is one of the few adhesive factors of enterohemorrhagic Escherichia coliO157:H7 associated with colonization of the intestine. E. coliO157:H7 strains possess two lpfloci encoding highly regulated fimbrial structures. Database analysis of the genes encoding the major fimbrial subunits demonstrated that they are present in commensal as well as pathogenic (both intestinal and extraintestinal) E. colistrains and in Salmonellastrains and that the lpfA1and lpfA2genes are highly prevalent among LEE (locus of enterocyte effacement)-positive E. colistrains associated with severe and/or epidemic disease. Further DNA sequence analysis of the lpfA1and lpfA2genes from different attaching-and-effacing E. colistrains has led us to the identification of several polymorphisms and the classification of the major fimbrial subunits into distinct variants. Using collections of pathogenic E. coliisolates from Europe and Latin America, we demonstrated that the different lpfAtypes are associated with the presence of specific intimin (eae) adhesin variants and, most importantly, that they are found in specific E. colipathotypes. Our results showed that the use of these fimbrial genes as markers, in combination with the different intimin types, resulted in a specific test for the identification of E. coliO157:H7, distinguishing it from other pathogenic E. colistrains.