Characterization of multidrug-resistant Salmonella enterica subsp. enterica Serovar Typhimurium var. Copenhagen and Typhimurium isolated from feedlot cattle.

The objective of this study was to characterize Salmonella enterica subsp. enterica Serovars Typhimurium and Typhimurium var. Copenhagen isolated from naturally infected feedlot cattle (n = 138) in North Dakota for antimicrobial resistance (AMR), presence of integrons and genotypic relatedness by use of PFgE assays. A panel of 15 selected antimicrobials and the Sensititre automated antimicrobial susceptibility test system (TREK Diagnostic Systems, westlake, Oh) were used. Class 1 and 2 integrons were targeted by PCR, using primers specific for the intI1 and intI2 genes. Pulsed field gel electrophoresis (PFgE) assays were performed by the E. coli Reference Center, Pennsylvania State University, University Park, PA. All 58 Salmonella isolates tested were resistant to ≥ 1 of the antimicrobials, with 56/58 (96.6%) showing multidrug resistance (resistant to