Serotypes, MIC-Based Antimicrobial Susceptibility, and Genotypic Diversity of Actinobacillus pleuropneumoniae Isolates from Diseased Pigs in Brazil

Actinobacillus pleuropneumoniae is a major swine pathogen that causes pleuropneumonia and leads to substantial economic losses due to mortality, impaired growth, and carcass condemnation. Nineteen serovars have been described, and their geographic distribution has been assessed using multiple typing approaches. High serovar diversity, together with limited cross-protective immunity, increases reliance on antimicrobial therapy for disease control. However, data on the genotypic diversity and antimicrobial susceptibility of A. pleuropneumoniae remain limited worldwide, and information on serovar distribution in Brazil is scarce. Here, we report serotyping, genotyping, and antimicrobial susceptibility profiling of A. pleuropneumoniae isolated from diseased pigs in Brazil. Eighty-five isolates from eight Brazilian states were analyzed; serovars 5 and 10 were the most prevalent (38.8% and 29.4%, respectively). Ceftiofur, spectinomycin, gentamicin, neomycin, tilmicosin, tulathromycin, and florfenicol showed good in vitro activity against the isolates. The highest resistance rates were observed for tylosin (98.8%), clindamycin (90.6%), chlortetracycline (67.1%), and oxytetracycline (67.1%), and multidrug resistance was detected in 55% of strains. SE-AFLP and PFGE revealed high genetic diversity, including among isolates of the same serovar, although a modest tendency to cluster by geographic origin and serovar was observed.