author(s)
Afaf Abdulrahman Yousif, Mustafa Salah Hasan, Thaar Mohammed Najim and Mohammed Ali Hussein

abstract
The main objective of this study was to detect the virulence of E. coli O157:H7 by using Congo red dye and to determine the pattern of antimicrobial susceptibility for twenty six isolates of E. coli O157:H7 obtained from Department of internal and preventive medicine/ College of Veterinary Medicine/ University of Baghdad isolated from diarrheic and non- diarrheic dogs found in Baghdad Province, the study extended from March 2015 to August 2015. Seven antimicrobial discs were used in this study Chloramphenicol (30µg), Ampicillin (10µg), Trimethoprim plus sulfa (1.25 µg), Ciprofloxacin (5µg), Erythromycin(15µg), Gentamycin (120 µg), Cephalexin (30 µg), Trimethoprim(5 µg). The result showed that 24 isolates gave a positive result for Congo red, whereas only two isolates give a negative result. Results of antimicrobial susceptibility showed that the isolates susceptible to Ciprofloxacin at a percentage (80.76%) followed by gentamycin and trimethoprim plus sulfa at a percentage (53.84 % ; 46.15 %) respectively. In conclusion, isolates of E. coli O157:H7 isolated from fecal samples from diarrheic and non-diarrheic dogs were having the multidrug resistant phenomena and most of isolates were positive to Congo red dye which indicated this organism as an invasive pathogen.