Background: Shiga toxin-producing Escherichia coli (STEC) strains are considered as one of the most important widespread food-borne pathogens, which cause diarrhea and life threatening diseases, such as hemolytic uremic syndrome, in humans. More recently, the STEC strains have also been incriminated to cause diarrhea and hemorrhagic colitis in calves; enteropathogenic E. coli (EPEC) also causes diarrhea in neonate animals. Objectives: This study aimed to study the prevalence and antibacterial resistance patterns of STEC and EPEC in fecal samples from diarrheic calves in Mashhad and Garmsar districts, Iran. Materials and Methods: A total of 115 fecal samples were collected from diarrheic animals, 75 from Mashhad and 40 from Garmsar districts. A total of 146 E. coli isolates were obtained from culture and subjected to multiplex-PCR assay targeting stx1, stx2, eaeA and ehly virulence genes. The antibacterial resistance patterns of the virulence-positive isolates were determined using disc diffusion method. Results: Eight samples (6.9%) carried the strains with positive results for at least one of the tested virulence genes. Five samples (4.3%) contained the stx-positive strains (STEC) and three (2.6%) carried the eaeA-positive and stx-negative strains, which were categorized as EPEC. In nine virulence-positive E. coli isolates, stx1 (n = 6) was the predominant virulence gene, followed by ehly (n = 5), eae (n = 4), and stx2 (n = 2). Antibacterial resistance patterns of virulence-positive isolates were also determined and nine resistance profiles were discriminated; higher rates of resistance were observed in isolates from Mashhad. Conclusions: This study indicated that other pathologic factors might play a more important role in calf diarrhea in the studied areas, but public health significance of these strains should not be overlooked.

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