Antimicrobial susceptibility of Actinobacillus pleuropneumoniae, Bordetella bronchiseptica, Pasteurella multocida, and Streptococcus suis isolated from diseased pigs in the United States and Canada, 2016 to 2020

Abstract

Objective: To report the in vitro susceptibility to veterinary antimicrobial agents of Actinobacillus pleuropneumoniae, Bordetella bronchiseptica, Pasteurella multocida, and Streptococcus suis isolated from diseased pigs in the United States and Canada from 2016 to 2020. Materials and methods: In vitro broth microdilution susceptibility testing for minimal inhibitory concentration values were performed using ten antimicrobial agents (ampicillin, ceftiofur, danofloxacin, enrofloxacin, florfenicol, penicillin, tetracycline, tilmicosin, trimethoprim-sulfamethoxazole, and tulathromycin) with A pleuropneumoniae (n = 250), B bronchiseptica (n = 602), P multocida (n = 874), and S suis (n = 1223) following methods and susceptibility breakpoints approved by the Clinical and Laboratory Standards Institute. Results: Actinobacillus pleuropneumoniae isolates were 100% susceptible to ceftiofur, florfenicol, and tulathromycin and P multocida isolates were 100% susceptible to ceftiofur. High rates of susceptibility (95% to > 99%) were observed for A pleuropneumoniae to tilmicosin; for P multocida to ampicillin, enrofloxacin, florfenicol, penicillin, tilmicosin, and tulathromycin; for S suis to ampicillin and florfenicol; and for B bronchiseptica to tulathromycin. Tetracycline exhibited low susceptibility rates against A pleuropneumoniae (0% to 10.6%), P multocida (23.2% to 38.2%), and S suis (0.8% to 2.1%). No susceptibility of B bronchiseptica to ampicillin (0%) and low rates of susceptibility to florfenicol (3.9% to 15.2%) were also observed. Implications: Under the conditions of this study, the predominant pathogens associated with swine respiratory disease in the United States and Canada, A pleuropneumoniae, B bronchiseptica, P multocida, and S suis collected during 2016 to 2020, display high rates of susceptibility to most veterinary antimicrobial agents.