Association of IS with Multidrug Resistance in Isolates from Cattle ().

is, globally, an important cause of human illness with beef being a significant attributable source. In the human patient, systemic infection requires antibiotic therapy, and when strains are multidrug resistant (MDR), no effective treatment may be available. MDR in bacteria is often associated with the presence of mobile genetic elements (MGE) that mediate horizontal spread of antimicrobial resistance (AMR) genes. In this study, we sought to determine the potential relationship of MDR in bovine isolates with MGE. The present study involved 111 bovine isolates obtained collectively from specimens derived from healthy cattle or their environments at Midwestern U.S. feedyards (2000-2001, = 19), or specimens from sick cattle submitted to the Nebraska Veterinary Diagnostic Center (2010-2020, = 92). Phenotypically, 33/111 isolates (29.7%) were MDR (resistant to ≥3 drug classes). Based on whole-genome sequencing (WGS; = 41) and PCR ( = 111), a MDR phenotype was strongly associated (OR = 186; < 0.0001) with carriage of IS, an IS-like Family transposase. In all 41 isolates analyzed by WGS ((31 MDR and 10 non-MDR (resistant to 0-2 antibiotic classes)), MDR genes were associated with carriage of IS, most often on an IncC type plasmid carrying . The typical arrangement was , , , , and flanked by IS. These results suggest that AMR genes in MDR isolates of cattle are frequently associated with IS and carried on IncC plasmids. Further research is needed to better understand the role of IS in dissemination of MDR strains.