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U.S. Department of Health and Human Services

Animal & Veterinary

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FDA Veterinarian Newsletter September/October 2001 Volume XVI, No V


The National Antimicrobial Susceptibility Monitoring System _ Enteric Bacteria (NARMS-EB) was established to provide descriptive data on the extent and temporal trends of antimicrobial susceptibility in zoonotic enteric pathogens from human and animal populations. Salmonella was chosen as the sentinel organism. As part of the 1999 study, 8,508 Salmonella isolates of animal origin were tested against 17 antimicrobial drugs using a SensititreTM custom designed microtiter plate. Minimal inhibitory concentrations (MICs) were determined for all antimicrobials. Animal sources of isolates included cattle, swine, chickens, turkeys, exotics, horses, dogs, and cats. These isolates were from both diagnostic and non-diagnostic submissions. Overall, all isolates were susceptible to Ciprofloxacin. The following percent sensitivity was observed for all other antimicrobials—Amikacin (>99.9%), Amoxicillin/clavulanic acid (88.4%), Ampicillin (81.9%), Apramycin (98.9%), Ceftiofur (96%), Ceftriaxone (97.7%), Cephalothin (92.3%), Chloramphenicol (90.1%), Gentamicin (90.8%), Kanamycin (87.7%), Nalidixic Acid (98.8%), Streptomycin (69%), Sulfamethoxazole (71.1%), Tetracycline (64.8%), and Trimethoprim/sulfa (96.6%). Breakpoints are not available for Florfenicol but the MIC50 and MIC90 were 4 and 8 ug/ml, respectively. For all antimicrobials, isolates collected from raw product were more susceptible than diagnostic isolates. One hundred twenty-five different serotypes were identified and the 5 most common serotypes were S. typhimurium (including var. copenhagen, n=1562), S. montevideo (n=618), S. heidelberg (n=602), S. kentucky (n=593), and S. derby (n=515). Overall, S. typhimurium had higher resistance to more antimicrobials followed by S. heidelberg and S. derby. These data provide information which can be used to analyze the development of resistance over time when compared to previous years.