Antimicrobial susceptibility of Actinobacillus pleuropneumoniae, Pasteurella multocida, Streptococcus suis, and Bordetella bronchiseptica isolated from pigs in the United States and Canada, 2011 to 2015

Objective: To report the susceptibility to veterinary antimicrobial agents of Actinobacillus pleuropneumoniae, Pasteurella multocida, Streptococcus suis, and Bordetella bronchiseptica isolated from pigs in the United States and Canada from 2011 to 2015. Materials and methods: In vitro broth microdilution susceptibility testing for minimal inhibitory concentration values were performed using 10 antimicrobial agents (ampicillin, ceftiofur, danofloxacin, enrofloxacin, florfenicol, penicillin, tetracycline, tilmicosin, trimethoprim-sulfamethoxazole, and tulathromycin) with Actinobacillu pleuropneumoniae (n = 312), P multocida (n = 855), S suis (n = 1201), and B bronchiseptica (n = 572) following methods and susceptibility breakpoints approved by the Clinical and Laboratory Standards Institute. Results: Actinobacillu pleuropneumoniae isolates were 100% susceptible to ceftiofur and florfenicol, and P multocida isolates were 100% susceptible to ceftiofur, enrofloxacin, and florfenicol. High rates of susceptibility (90% to > 99% susceptible) were observed for A pleuropneumoniae to enrofloxacin and tulathromycin, for P multocida to ampicillin, penicillin, tilmicosin, and tulathromycin, for S suis to ampicillin, ceftiofur, and florfenicol, and for B bronchiseptica to tulathromycin. Tetracycline exhibited low susceptibility rates against A pleuropneumoniae (0% to 6% susceptibility), P multocida (22.3% to 35.3%), and S suis (0% to 1.3%). No susceptibility of B bronchiseptica to ampicillin (0%) and low rates of susceptibility to florfenicol (5.4% to 23.5%) were also observed. Implications: Under the conditions of this study, high rates of susceptibility to most veterinary antimicrobial agents continue to be seen for A pleuropneumoniae, P multocida, S suis, and B bronchiseptica, the predominant pathogens associated with swine respiratory disease in the United States and Canada.