Characterization of virulence genes of non-O157 Shiga toxin-producing Escherichia coli isolates from two provinces of Iran.

Shiga toxin-producing Escherichia coli (STEC) include O157:H7 and non-O157 serotypes. The public health impact of STEC infections is high because of their ability to cause severe infections. We characterized our STEC strains isolated from diarrheal and asymptomatic persons in northern and southwest Iran. The 29 STEC strains were examined for the presence of virulence genes by polymerase chain reaction (PCR) and their H type was analyzed by PCR-restriction fragment length polymorphism (RFLP) of the fliC gene. Moreover, the adherence properties of these strains were checked by HeLa cell adherence assay. The presence of non-O157 isolates under these conditions was again verified. The stx1 gene was present in 93% of the isolates, and the gene encoding intimin (eae) was not found to be present among the isolates. Almost all of the STEC isolates, with the exception of three, were non-adherent upon tissue culture assay. The serogrouping revealed the presence of seven different O types among non-O157 isolates. PCR-RFLP results for the fliC gene and classical serology examination with H antisera indicated the presence of nine different H types. In this study, three new serotypes of non-O157:H7 (i.e., O25:H3, O85:H32, and O162:H21) were found to be Shiga toxin producers. These findings reconfirm the results of our previously reported studies showing that non-O157:H7 serotypes are more prevalent under the present conditions. More detailed characterization of these isolates will require additional genetic studies.