Antimicrobial drug resistance and molecular characterization of Salmonella isolated from domestic animals, humans, and meat products.

OBJECTIVES 1) To characterize and determine genotypic relatedness of Salmonella serovars commonly isolated from domestic animals and humans in North Dakota, and 2) to assess their role in transferring antimicrobial resistance (AMR) to humans. MATERIALS AND METHODS A total of 434 Salmonella isolates obtained from 1) feces of apparently healthy feedlot, range, and dairy cattle in North Dakota; 2) clinical samples from sick or dead animals submitted to North Dakota State University-Veterinary Diagnostic Laboratory (2000-2005); 3) previous meat product surveillance studies in North Dakota; and 4) 179 samples from human patients in North Dakota (2000-2005) by the North Dakota Department of Health were studied. The isolates were initially serotyped and later genotyped by pulsed-field gel electrophoresis (PFGE) to investigate their relatedness. The National Antimicrobial Resistance Monitoring Systems panel was used to compare AMR profiles of animal and human isolates to assess a possible role of domestic animals in transfer of AMR to humans. RESULTS Salmonella Typhimurium was the predominant serotype in both humans (13.4%) and domestic animals (34.3%), followed by Newport in animals (2.6%) and human (3.9%). Salmonella Arizona (0.7%), Salmonella Give (0.9%), and Salmonella Muenster (3.5%) were isolated from sick or dead animals. PFGE results confirmed occurrence of similar Salmonella genotypes in both domestic animals and humans. AMR profiles showed that most animal strains were multidrug resistant. A single human isolate had PFGE and multidrug resistance profiles similar to a major cattle genotype, suggesting a possible AMR transmission from cattle to humans. CONCLUSION AND APPLICATION: Similar Salmonella genotypes were infecting domestic animals and humans in North Dakota. The AMR levels were higher in domestic animal isolates than in humans, implying that the occurrence of AMR in animal isolates may not translate directly into AMR in human isolates in North Dakota. This is helpful in determining future policies regarding antimicrobial drug use in domestic animals and humans.