Antibiogram use on dairy cattle for bovine respiratory disease: Multidrug resistance in Pasteurella multocida and Mannheimia haemolytica in California dairies

Abstract

Multidrug-resistant (MDR) bovine respiratory pathogens can significantly decrease treatment success and have an effect on dairy farm productivity. Although antibiograms have emerged as a tool to support empirical decision making for disease treatment, the prevalence of MDR isolates on a farm can have a negative effect on the selection of the best antibiotic treatment using antibiogram data. This study aimed to characterize the MDR profile of Pasteurella multocida and Mannheimia haemolytica isolates from the deep nasopharyngeal swabs of calves, heifers, and cows diagnosed with bovine respiratory disease (BRD) over 2 yr. For this purpose, animals were sampled in a repeated cross-sectional study from 3 large dairy farms in Northern California. From this study, a total of 146 P. multocida and 63 of M. haemolytica isolates were isolated and tested for antimicrobial susceptibility. Our results showed that, overall, a small fraction of the animals in the study had MDR P. multocida (15%) and M. haemolytica (17%). The prevalence of MDR P. multocida isolates was comparable between calves (14%), heifers (19%), and cows (12%), whereas MDR M. haemolytica was most prevalent in heifers (40%) followed by calves (4%). No MDR M. haemolytica was detected in the isolates from cows. Farm effect had the most significant association with MDR BRD pathogens, with 1 farm accounting for 94% of all MDR isolates of the study, while season had a minor association with MDR. The most common antimicrobial resistance drug classes across MDR pathogens were macrolides, phenicols, quinolones, and tetracyclines. Prevalence of resistant isolates to tetracyclines represented the greatest disparity between the 2 BRD pathogens evaluated, with P. multocida isolates having a higher percentage of resistance (71.8%) when compared with M. haemolytica (22.2%). In conclusion, there was a low prevalence of MDR in both P. multocida and M. haemolytica in the study, but farm management and the age of the animals increased the odds of MDR prevalence. These factors should be considered when generating antibiogram reports for BRD treatment to account for the potential prevalence of MDR isolates.