Title: In vitro susceptibility of bovine Salmonella enterica to cefquinome and cefepime in the U.S. Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 26, 2007
Publication Date: December 17, 2007
Citation: Cray, P.J., Frye, J.G., Haro, J.H., Rose, M. In vitro susceptibility of bovine Salmonella enterica to cefquinome and cefepime in the U.S. [abstract]. 2nd Symposium on Antimicrobial Resistance in Animals and the Environment. 27. Technical Abstract: Background: The purpose of this study was to monitor the in-vitro susceptibility of bovine Salmonella enterica, isolated in the US, against the 4th generation cephalosporins (4-GC) cefquinome and Cefepime from 2000 through 2006. Cefquinome is licensed for therapeutic use in cattle and swine in Europe, and cefepime is licensed for therapeutic use in human medicine (The Sanford Guide, 2005). Methods: Salmonella enterica isolates (n=4,685) obtained from cattle at federally inspected slaughter/processing plants during 2000 - 2006 and submitted to the animal arm of the National Antimicrobial Resistance Monitoring System – Enteric Bacteria (NARMS) were tested for minimum inhibitory concentrations (MICs) using a custom panel of antimicrobials, and a second panel with cefquinome and cefepime (CLSI, 2002). Isolates collected from 2000-2004 with reduced susceptibility to ceftriaxone (MICs > 32 ug/ml) were tested for the presence of extended spectrum beta-lactamases (ESBLs). Results: The MIC50 of the 4-GC cefquinome and cefepime against all bovine Salmonella enterica isolates remained at 0.06 µg/ml throughout the seven-year period, except during 2002 when cefquinome activity increased by one dilution to 0.12 µg/ml before decreasing again in 2003. The MIC90s for both cefquinome and cefepime was 0.12 µg/ml in 2000, which increased to 1.0 µg/ml and 0.5 µg/ml, respectively, for 2002, then decreased to 0.5 µg/ml and 0.25 µg/ml for cefquinome and cefepime, respectively, in 2003 and 2004. Subsequently, the MIC90s for both cefquinome and cefepime increased again to 1.0 µg/ml and 0.5 µg/ml, respectively, for 2005, and decreased to 0.5 µg/ml and 0.25 µg/ml in 2006. The one dilution variance between years is most often attributed to the varying MICs which are dependent upon serotype. Collectively, the most common serotypes throughout the seven year period were S. Montevideo, S. Typhimurium (including var. 5-), and S. Newport. The majority of isolates from years 2000 – 2004 with reduced susceptibility to ceftriaxone carried the blaCMY-2 gene, and no ESBL genes were detected. Discussion and Conclusions: Bovine non-diagnostic Salmonella enterica isolates remained highly susceptible to the veterinary 4-GC cefquinome and the human 4-GC cefepime over the seven-year observation period. Additional ESBL testing is being conducted on isolates from 2005 and 2006 with reduced susceptibility to ceftriaxone.