Challenge studies in volunteers using Escherichia coli strains with diffuse adherence to HEp-2 cells

diarrhea in children in some but not all epidemiologic studies. To investigate its diarrheagenic potential, two strains of DA E. coli were fed to adult volunteers in doses of lOS-10to colony-forming units. None of22 volunteers who received strain 57-lor of21 who received strain C1845 developed symptoms of diarrhea as defined for this study. All volunteers shed the challenge DA E. coli in their stools. Duodenal string cultures were positive in some volunteers only at the highest doses. Only 6 developed IgG or 19A antibodies to whole DA E. coli. Thus, the pathogenic poten-tial of DA E. coli could not be shown in this model. Further studies are needed to characterize potential virulence factors of DA E. coli that might distinguish a pathogenic subset. Several categories of Escherichia coli have been identified that cause diarrhea in various epidemiologic settings and by several pathogenic mechanisms: enterotoxigenic, enteroinva-sive, enterohemorrhagic, and enteropathogenic E. coli (EPEC) [1]. More recently, two other distinct categories of putatively diarrheagenic E. coli have been defined based on their pat-tern of adherence to HEp-2 cells in culture [2]. Three pat