Characterization of Enteroadherent-Aggregative Escherichia coli, a Putative Agent of Diarrheal Disease

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Abstract
Escherichia coli that exhibit the aggregative pattern of adherence to HEp-2 cells (entero adherent-aggregative E. coli [EA-AggEC]) have been epidemiologically incriminated as a causeof diarrhea. We undertook a preliminary microbiological and pathogenetic characterization of 42 isolates of this putative pathogen. The strains were negative by tests with DNA probes for enteropathogenic, enterotoxigenic, entero invasive, and entero-hemorrhagic E. coli and, by serotype, did not fit these categories. Thirty-nine of 42 strains had a 55–65-megadalton plasmid; many shared DNA homology. With one representative strain, plasmid transfer was accompanied by transfer of smooth lipopolysaccharide, fimbriae expression, and the aggregative property. EA-AggEC caused characteristic lesions in rabbit and rat ileal loops. The intestinal lesions and (Shiga-like) limb paralysis and death in rabbits inoculated with live organisms suggest toxin involvement; assays for Shiga-like toxins were negative. These preliminary results support the contention that EA-AggEC may represent a distinct category of diarrheagenic E. coli.