Introduction and Objectives Enterotoxigenic E. coli (ETEC) is considered as one of the most common causes of infectious diarrhea in calves, striking the first week of age. The heat stable toxin (STa) of ETEC is the primary mediator of chloride secretion which leads to Secretory diarrhea. Besides, almost all ETEC bacteria are known to ad- here to receptors on the small intestinal epithelium via their fimbriae, (F5 (K99) and F41). This study was undertaken to investigate the genotypic screening of virulence genes in ETEC E. coli isolated from dairy neonatal calves of Hamedan city. Materials and Methods During March to August 2016, 120 rectal swab samples, 60 from clinically healthy and 60 from diarrheic calves, were collected from 1-7 days old calves belonging to 8 dairy farms in Hamedan city. E. coli was isolated using routine bacteriological methods and screened by the multiplex PCR assay for the presence of virulence genes characteristic for ETEC. Results E. coli isolates were recovered nom 19.16% (23) samples, 39.13% (9) in healthy and 60.86% (14) in diarrheic cases. Overall, PCR Results showed that 12 (52. 17%) isolates carried F41 gene and 1 (4.34%) possessed sta gene, while 1 isolate (4.34%) gave positive amplicon both for sta+F5 genes, 1 (4.34%) carried sta+F4l genes, l had F5+F4l genes and 7 carried sta+F5+F4l genes. Conclusion In total, diverse virulence gene profiles were detected from which isolates with the genetic profile sta+F5+F4l was the most prevalent. In addition, 56.52% (13 isolates) were proven not to be toxigenic as they did not possess the STa enterotoxin gene.
