Extended spectrum cephalosporins (ESC) represent very important antimicrobial agents in both human and animal medication. They can be used as drugs of last resort for children and elderly infected with salmonella. Recent reports have shown that resistance to these antimicrobials  have appeared in salmonella found in pig diarrhea. This study attempts to find out if this resistance in pig E.coli is due to chromosomal mutations or due to resistance genes located on plasmids which may be exchanged between bacteria, and to characterize the transferable plasmids associated with ESC resistance and to compare the ESC resistance plasmids from porcine E.coli with those from salmonella. Three different types of plasmids encoding resistance to ESCs were found in pig diarrhea, all three carry the same ESC resistance gene and were transferable from E.coli to salmonella. Two of these plasmids are already known to occur in E.coli and salmonella in animals. These two have been found on several farms and in pathogenic and non-pathogenic E.coli, the third  has not been seen anywhere else and appears to be new. This study shows that plasmid-borne transferable resistance to ESCs has emerged in porcine E.coli in Ontario. The potential for medicating swine for this may be eroding and there is potential for it to transfer to salmonella.