Antimicrobial Resistance in Bovine Respiratory Disease Pathogens: A Systematic Review and Analysis of the Published Literature.

Bovine respiratory disease (BRD) is the most significant disease challenge in the feeder cattle industry in North America. Antimicrobials are commonly administered in BRD cases due to the role of bacterial pathogens. However, reports of antimicrobial resistance (AMR) in these pathogens raise concerns regarding their long-term effectiveness to treat BRD cases. A systematic literature review was conducted to summarize AMR in North American BRD pathogens and determine if changes in AMR prevalence over time could be identified for antimicrobials routinely used for treatment and control of BRD. Generalized linear models were used to test associations between the proportion of resistant isolates for each of the three bacterial agents and antimicrobial agent, isolation year, and timing of sample collection. The antimicrobial agent and timing of sample collection were significantly associated with the proportion of antimicrobial resistant isolates, with increased probability of resistance to tulathromycin seen in (24.08%) and (8.19%) and increased resistance to tildipirosin in (21.48%), while samples collected at arrival demonstrated a lower proportions of resistant bacteria. Trends over time could not be evaluated due to the limited number of published studies. These findings highlight the differences in AMR seen between antimicrobials, BRD pathogens, and sample types and emphasize the need for continued AMR surveillance.