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EHEC is an emergent pathogen which causes haemorrhagic colitis and complications of the potentially fatal HUS. The main virulence factors are the phage-encoded Shiga toxin and the intimate attachment to host cells. Shiga toxin affects cells not only by inhibiting protein biosynthesis but also through the induction of signalling cascades leading to apoptosis. The locus of enterocyte effacement (LEE) encodes a type III secretion system that translocates bacterial effector proteins into the host cell cytoplasm. Intimate attachment is mediated through interactions of the bacterial outer-membrane protein Intimin and the translocated intimin receptor (Tir) on the host cells. Recently, a very rare serogroup strain in humans of E. coli 0104, which carries a stx2a gene in a typical type of EAggEC, appeared in EU and caused a big outbreak of haemorrhagic colitis and HUS.

Shiga-like-toxin-producing Esherichia coli O128:HNM were isolated from feces of a one-year-old boy with diarrhea and abdominal pain on July, 2002, and a 11-month-old girl with diarrhea and fever on June, 1997. None of other enteropathogenic bacteria including Salmonella were isolated. E. coli O128:HNM isolates from both patients carry stx2f and eaeA gene, but not stx1, stx2, aggR, bfpA, esth, estp, invE, astA, ureC and hlyA gene. As far as we know, this may be the first report indicating that E. coli O128:HNM carrying stx2f gene were isolated from patients in Japan.

To clear the route of STEC (Shiga toxin-producing Escherichia coli) infection to humans, we examined the serotype. Shiga toxin genotype and eae gene of STEC strains from humans and various animals. The most predominant serotype originated from humans was O157:H7, followed by O26:H11, and other serotypes were O91:H21, O103:H2, O111:NM, O121:H19, etc. The eae gene was found in 79 of 93 strains from human origin. The serotypes of STEC from cattle were significant by similar to that of STEC from humans. The eae gene was found in 44 of 87 strains from cattle. Shiga toxin genotypes possessed O157 strains from humans and cattle, were divided into six groups, stx1, stx2, stx2c, stx1 + stx2, stx1 + stx2c and stx2 + stx2c. Moreover, frequency rates of Shiga toxin genotypes of O157 were also similar to both human and cattle origins. The serotypes of STEC from sheep were also a little similar to that of STEC from humans. Seven of 8 strains from deer possessed stx2d gene that the strains from humans seldom possessed, and none of the strains possessed eae gene. In STEC originated from swine, 15 of 25 strains were O139:H1 that Shiga toxin genotype was stx2e. It was thought that the sources of STEC infection to human are cattle and sheep, and deer and swine had little possibility to human STEC infection.