Little is known about antimicrobial resistance in bacteria from pet dog populations in Canada. Three hundred and sixty-three 'E. coli' isolates were collected from cases of canine urinary tract infection in Ontario and Que?bec, and their susceptibility to 15 antimicrobial agents was assessed. Resistance to ampicillin was the most frequent; no isolates were resistant to amikacin, The overall frequency of antimicrobial resistance was relatively high, 34% overall; there was no apparent difference between Ontario and Quebec. Multiresistance was common (17%), as was [beta]-lactam resistance (20%). 'bla'TEM, 'bla'CMY-2 , 'bla'CTX-M and 'bla' OXA-1 but not 'bla'SHV genes were detected in isolates resistant to [beta]-lactams. Further characterization of ' bla'CTX-M revealed two 'bla'CTX-M-14 and 'bla'CTX-M-15 variants. Isolates from two different canine patients belonged to a 'bla'CTX-M-15 -carrying O25:H4 clone associated worldwide with human infections.