f For exhaustive detection of diarrheagenic Escherichia coli, we previously developed a colony-hybridization method using hydrophobic grid-membrane filters in combination with multiplex real-time PCR. To assess the role of domestic animals as the source of atypical enteropathogenic E. coli (aEPEC), a total of 679 samples (333 from foods, fecal samples from 227 domestic animals, and 119 from healthy people) were examined. Combining 48 strains previously isolated from patients and carriers, 159 aEPEC strains were classified by phylogroup, virulence profile, and intimin typing. Phylogroup B1 was significantly more prevalent among aEPEC from patients (50%) and bovine samples (79%) than from healthy carriers (16%) and swine strains (23%), respectively. Intimin type ␤1 was predominant in phylogroup B1; B1-␤1 strains comprised 26% of bovine strains and 25% of patient strains. The virulence profile groups Ia and Ib were also observed more frequently among bovine strains than among porcine strains. Similarly, virulence group Ia was detected more frequently among patient strains than strains of healthy carriers. A total of 85 strains belonged to virulence group I, and 63 of these strains (74%) belonged to phylogroup B1. The present study suggests that the etiologically important aEPEC in diarrheal patients could be distinguished from aEPEC strains indigenous to humans based on type, such as B1, Ia, and ␤1/␥1, which are shared with bovine strains, while the aEPEC strains in healthy humans are different, and some of these were also present in porcine samples.

The etiological roles of diarrheagenic Escherichia coli (DEC), including enteroaggregative E. coli (EAggEC), diffusely adherent E. coli (DAEC) and EAST1EC---a strain of E. coli that possesses no diarrheagenic characteristics other than the EAggEC heat-stable toxin 1 (EAST1) gene---remain controversial. To clarify the prevalence of DEC among healthy individuals in Osaka City, Japan, and to compare the virulence properties of strains previously isolated from diarrheal patients, fecal specimens were examined for DEC. Isolation rates of Shiga toxin-producing E. coli, enterotoxigenic E. coli and EAggEC were significantly lower among healthy adults than sporadic adult patients. There were no differences in enteropathogenic E. coli (EPEC), DAEC and EAST1EC between patients and healthy carriers. Subtyping of the intimin gene (eae) of EPEC, and measuring the IL-8 inductivity of DAEC on epithelial cells could provide criteria to distinguish strains in diarrheal patients from those in healthy carriers. Proper criteria should be established in order to diagnose subtypes of DEC as causative agents.