#03-068

Complete

Date Full Report Received

10/20/2004

Date Abstract Report Received

06/24/2009

Investigation

Institution:
Primary Investigator:

In the presence of antibiotics in the feed, pigs became readily colonized with E. coli resistant to the antibiotic ceftiofur. Some E. coli harboured the specific gene blaCMY-2, known to confer resistance to this drug, while the mechanism of resistance of other isolates was not determined. Importantly, despite intense antibiotic selective pressure (i.e. subtherapeutic doses of antibiotics in the feed and therapeutic treatment with ceftiofur), neither the transfer of resistance from Salmonella to E. coli nor from E. coli to Salmonella could be detected in the live animal. Transmission of ceftiofur resistant bacteria appears to occur readily and from multiple sources, but the gastrointestinal tract of weaned pigs dose not appear to be a site of significant genetic transfer of plasmids encoding the blaCMY-2 gene. Alternative sources and reservoirs of emergence of these organisms (such as the environment) must be explored. Ceftiofur resistant Salmonella in swine are most likely to appear due to the transmission of the Salmonella which already encode the blaCMY-2 gene, rather than the acquisition of this resistance gene from other bacteria in the gastrointestinal tract of swine. Therefore, emphasis should be placed on controlling the dissemination and transmission of bacteria that are already resistant to antibiotics from farm to farm.