EPIDEMIOLOGY, ECOLOGY, AND MOLECULAR GENETICS OF ANTIMICROBIAL RESISTANCE IN PATHOGENIC AND COMMENSAL BACTERIA FROM FOOD ANIMALS
Location: Bacterial Epidemiology and Antimicrobial Resistance
Title: Antimicrobial Resistance in Salmonella Isolates Recovered from Cattle at Slaughter
Submitted to: Proceedings of the International Conference on Emerging Infectious Diseases
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2008
Publication Date: March 16, 2008
Citation: Cray, P.J., Frye, J.G., Rose, M., Anandaraman, N., Haro, J.H. 2008. Antimicrobial Resistance in Salmonella Isolates Recovered from Cattle at Slaughter. Proceedings of the International Conference on Emerging Infectious Diseases. (79)92.
Background: Since 1997, the animal arm of the National Antimicrobial Resistance Monitoring System (NARMS) has monitored changes in antimicrobial susceptibilities of Salmonella isolates from animal origin. Additionally, since 2000, susceptibility of bovine Salmonella isolates collected in the US has been monitored against the 4th generation cephalosporins (4-GC) cefquinome, exclusively developed for veterinary medicine, and cefepime. Cephalosporins are used extensively to treat human and cattle diseases. To identify emerging resistance patterns, resistance trends to the cephalosporins (ceftriaxone, ceftiofur, cefoxitin and cefquinome) in Salmonella isolates collected from cattle at slaughter were analyzed.
Methods: Salmonella enterica isolates (n=7,199) obtained from cattle at federally inspected slaughter/processing plants during 1997 - 2006 and submitted to NARMS were tested for minimum inhibitory concentrations (MICs) using a custom panel of antimicrobials. Isolates collected during 2000-2006 (n=4,685) were also tested on a second panel with cefquinome and cefepime.
Results: Resistance to ceftriaxone remained below 1%, except in 2005 when resistance increased to 2.1%. From 1997 to 2005, resistance to ceftiofur increased from 0% to 21.6%, with the exception of 2004 when it decreased to 13.3%. Resistance decreased again in 2006 to 18.9%. A similar pattern was observed for cefoxitin (testing started in 2000). Cefoxitin resistance increased from 2000 to 2005 from 9.1% to 19.8%, except in 2004 when it decreased to 13.2%. As with ceftiofur, a decrease was observed in 2006 when resistance was 17.9%. From 2000 to 2006 the MIC50 of cefquinome remained at 0.06 µg/ml, except in 2002 when the MIC50 increased by one dilution to 0.12 µg/ml. The highest MIC90 for cefquinome was 1.0 µg/ml in 2002 and 2005. MICs of cefepime were generally about one dilution step below those of cefquinome. Changes in resistance for all drugs were in large part driven by serotype, particularly S. Newport, Reading, Typhimurium and Agona.
Conclusions: Salmonella enterica isolates remained highly susceptible to the human 3-GC ceftriaxone and the 4-GCs cefquinome and cefepime. Overall, an increase in both veterinary 3-GC ceftiofur and human 2-GC cefoxitin has been observed at similar levels and appears to be serotype dependent.