Serovar and multilocus sequence typing analysis of Pasteurella multocida from diseased pigs in Taiwan

Pasteurella multocida causes progressive atrophic rhinitis and suppurative bronchopneumonia in pigs, which results in severe economic losses in swine industry. This study aimed to determine the serovar, genotype and prevalence of toxA virulence gene of Pasteurella multocida isolates collected in Taiwan. A total of 164 Pasteurella multocida isolates from 161 diseased pigs were characterized by serotyping, multilocus sequence typing (MLST), antimicrobial susceptibility testing, and the presence of virulence gene (toxA) and antibiotic resistance gene (floR).

The majority of Pasteurella multocida strains were serovar D:L6 (48.2%; 79/164) followed by A:L6 (28.7%; 47/164) and A:L3 (19.5%; 32/164). More than 80% of strains carrying toxA gene belonged to serovar A:L6 (82.6%; 19/23). The MLST data showed five sequence types (STs), where multi-host ST10 was the most dominant. Most Pasteurella multocida strains of multi-host ST10 were serovar A:L6 (93.9%; 31/33), which suggested that STs were highly associated with specific serovars. Most of the floR-carrying Pasteurella multocida strains belonged to serovar D:L6 with significantly high resistance to some antimicrobial agents, especially florfenicol.

This study demonstrated that serovar D:L6 and multi-host ST10 was the most prevalent Pasteurella multocida strain in Taiwan. A:L6 accounted for the majority of toxA-positive strains and the presence of floR gene may be responsible for the antimicrobial resistance to florfenicol.