ARS | Publication request: Prevalence, Distribution and Characterization of Ceftiofur Resistance in Salmonella enterica Isolated from Animals in the U.S. from 1999 to 2003

Submitted to: International Journal of Antimicrobial Agents
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 23, 2007
Publication Date: July 1, 2007
Citation: Frye, J.G., Cray, P.J. 2007. Prevalence, Distribution and Characterization of Ceftiofur Resistance in Salmonella enterica Isolated from Animals in the U.S. from 1999 to 2003. International Journal of Antimicrobial Agents. 30(2):134-142.

Interpretive Summary: Extended-spectrum cephalosporins are used to treat systemic Salmonella infections in children. Salmonella resistant to these antibiotics are found in humans and animals; however the impact that animals have on resistance in human infections is unknown. To investigate this, Salmonella enterica animal isolates from 1999 to 2003 were analyzed. Of 34,411 isolates, 3,749 (10.9%) were resistant and percent resistance rose steadily from 4.0% in 1999 to 18.8% in 2003. Cattle (17.6%), horses (19.2%) and dogs (20.8%), were higher than average, but turkeys (6.8%), chickens (7.1%), eggs (3.6%), and swine (4.6%) were lower. Clinical isolates were also higher at 18.5% while on-farm (3.4%) and slaughter (7.1%) isolates were lower than average. Characterization of 125 isolates showed that 82% of the cephalosporin resistance was due to a gene encoded on large, self transmissible plasmids. This information helps determine the impact of cephalosporin use in animals on pharmaceutical, agricultural and the human heath industries.

Technical Abstract: Resistance to extended-spectrum cephalosporins is potentially serious in the treatment of systemic Salmonella infections. Resistant isolates have been found in humans and animals; however the role that agricultural practices play in the development of resistance and spread to humans is unknown. To help determine this, 34,411 animal isolates collected from 1999 to 2003 were analyzed. Resistance to cephalosporins over that time rose steadily from 4.0% in 1999 to 18.8% in 2003, with an average of 10.9%. Animal sources with greater resistance included cattle (17.6%), horses (19.2%) and dogs (20.8%), but turkeys (6.8%), chickens (7.1%), eggs (3.6%), and swine (4.6%) had less resistant isolates than average. Clinical isolates were also much higher (18.5%), while on-farm isolates (3.4%) and slaughter isolates (7.1%) were less resistant. Seventy-six serotypes had cephalosporin resistance but five serotypes (Newport, Typhimurium, Agona, Heidelberg, and Kentucky) accounted for 80% of resistant isolates. Analysis of a subset of isolates showed that 82% of the cephalosporin resistance was due to the blaCMY-2 gene encoded on large (120-200 kb), self transmissible plasmids. These data suggest that the level of Salmonella cephalosporin resistance is increasing due to the spread of plasmids carrying resistance genes to a range of serotypes in several host animals.