RESUMEN
Seventy poultry farms' drinking water was tested for Escherichia coli contamination in Qom province in Iran. The cases of colibacillosis from positive farms were also collected and tested. The isolates were examined for serotype, detection of virulence genes by multiplex PCR and antibiotic resistance. Thirty poultry farm water samples were E. coli positive [18.57%], although 13 E. coli isolates were recovered from carcasses of related farms. The isolates belonged to O2 serogroup and one O157, with approximately 29% of the strains being non-typeable. Two isolates from water and carcasses were serotyped O2 and one sample serotyped O157, which needs to be further studied. The PCR method was on the basis on showing virulence genes of espB, stxl, stx2 genes were common in a sample from both water and carcass, although five samples from both water and carcass shared a stxl gene as well. All isolates showed maximum sensitivity and resistance to lincospectine and tetracycline, respectively