Pathotypes of bovine verotoxigenic Escherichia coli isolates producing attaching/effacing (AE) lesions in the ligated intestinal loop assay in rabbits

Effacement of the microvilli and intimate attachment to the enterocytes (AE lesions) are two common properties of enteropathogenic (EPEC) and many verotoxigenic (VTEC) E. coli isolates from humans and animals. However not all of the several chromosomal and plasmidic genes and loci involved in the pathogenesis of the human EPEC strain E2348/69 are present in EPEC and VTEC isolates from animal species. We here report that in addition to verotoxin-encoding genes, bovine VTEC isolates harbour a variant of the original eaeA gene, confirming previous results, but neither the eaf nor the bfp loci which are involved in early attachment stage, and that not all of them possess an eaeB gene, as determined by the colony hybridization assay. Have these bovine VTEC isolates lost some of the loci or are they not necessary for the production of AE lesions in vivo ? We also report the results of the ligated intestinal loop assay in rabbits with several bovine VTEC isolates. The production of AE lesions was correlated with the presence of an eaeA gene, but not with the presence of an eaeB gene, and was of course independent of the presence of the eaf and bfp loci. The eaeA-negative VTEC isolates produced no AE lesions. Either the eaeB gene is unnecessary for the production of AE lesions in the rabbit ligated intestinal loop assay or bovine VTEC possess other loci coding for similar functions. As to the adhesins involved in the early attachment step of bovine VTEC, they are most probably specific to cattle.