191 * Corresponding author: Department of Pathobiology, Faculty of Veterinary Medicine, Semnan University, Sem- nan, Iran. Telefax: +98233344985 E-mail: hstaji@semnan.ac.ir Distribution of Shiga toxin genes subtypes in B 1 phylotypes of Escherichia coli isolated from calves suffering from diarrhea in Tehran suburb using DNA oligonucleotide arrays Hamid Staji 1* , Alfreda Tonelli 2 , Abbas Javaheri-Vayeghan 1 , Emad Changizi 1 , Mohammad Reza Salimi-Bejestani 1 1 Department of Pathobiology, Faculty of Veterinary Medicine, Semnan University, Semnan, Iran. 2 Istituto Zooproflattico Sperimentaledell'Abruzzo e del Molise " G. Caporale" , Research and Development, Campo Boario, 64100 Teramo, Italy. Received: January 2015, Accepted: June 2015 ABSTRACT Background and Objectives: Shiga toxin-producing Escherichia coli (STEC) have emerged as human pathogens and con- tamination via animal origin has been a major public health concern. We compared the distribution of phylogenetic groups and prevalence of stx gene variants among the pathogenic strains of Escherichia coli isolated from feces of diarrheatic calves in Tehran suburb farms. Materials and Methods: In this study we screened 140 diarrheatic calves (1-15 days old) for E. coli strains during a 3 months period of time. The isolated strains were grouped into different phylotypes according to the presence of chuA, yjaA and TSPE4.C2 genes. Then, the prevalence of stx gene subtypes was evaluated in the B 1 phylotypes. Results: From diarrheatic calves, 51 bacterial isolates were biochemically identifed as E. coli and 31 isolates out of 51 were considered B 1 phylotype using DNA Microarray technology. Of these isolates, 20 contained stx 1 a and stx 1 b and one harbored all mentioned variants of stx genes except stx 2 b 2 . Conclusion: This study showed that in Tehran suburb, the B 1 phylotype of E. coli is prevalent as a causative agent of diarrhea in calves and the prevalence of stx 1 gene subtypes is dominant in comparison with other subtypes. Considering the possibility that these stx genes can be spread to other strains, bovine E. coli strains are an important source of stx genes for other strains and further study and surveillance seems to be required for the exact identifcation of virulence profle of E. coli phylotypes in different hosts. Keywords: Escherichia coli, calf diarrhea, B1 phylotype, shiga-like toxin subtypes, Tehran suburb meat producing domestic animals, especially at the frst weeks of life and ruminants are one of the res- ervoirs of Shiga like toxin producing E. coli (STEC), excreting this infectious agent in feces and environ- ment(1). STEC is a public health threatening germ causing sporadic and outbreaks of human problems including diarrhea, hemorrhagic colitis and Hemo- lytic-Uremic Syndrome (HUS) characterized by acute renal failure, microangiopathic hemolytic anemia and thrombocytopenia. The ability of STEC Volume 7 Number 4 (August 2015) 191-197 ORIGINAL ARTICLE INTRODUCTION Escherichia coli is one of the most important agents causing gastrointestinal tract infection in