Actinobacillus pleuropneumoniae in Korea (2015-2025): serovar distribution, toxin gene profiles, antimicrobial resistance, and identification of an apxIICA-deficient serovar 15 profile

초록

Importance: Despite Actinobacilluspleuropneumoniae (APP) being a major cause of porcine pleuropneumonia in Korea, decade-long integrated data on serovar distribution, toxin gene profiles, and antimicrobial resistance remain limited, thereby constraining evidence-based prevention and control strategies. Objective: To provide a decade-long molecular and phenotypic characterization of APP isolates from Korean pig farms, focusing on the serovar distribution, apx-based toxin-gene profiles, and antimicrobial susceptibility. Methods: Between 2015 and 2025, 1,215 pneumonic lung samples from 965 pig farms yielded 132 APP isolates. The species identity was confirmed by 16S rRNA sequencing. The serovars were determined using capsule polysaccharide (CPS) gene-based multiplex polymerase chain reaction (PCR). Toxin genes (apxIA-apxIVA) were profiled, and the antimicrobial susceptibility to 29 agents was assessed by broth microdilution according to the Clinical and Laboratory Standards Institute guidelines. Results: Serovar 1 was predominant (66.7%), followed by serovars 5 (17.4%) and 2 (6.8%). CPS multiplex PCR identified three isolates (2.3%) as serovar 15, which displayed heterogeneous toxin gene profiles, including apxIICA-deficient profiles. Most isolates exhibited classical repeats-in-toxin operon arrangements, suggesting ongoing diversification of toxin gene profiles. High resistance rates were observed for oxytetracycline (90.9%) and florfenicol (50.8%), and recurrent multidrug-resistant combinations were frequently detected. Conclusions and Relevance: Serovar 1 is dominant in Korea, but the emergence of atypical toxin gene profiles in serovar 15 may carry immunological implications. Persistent resistance to older drug classes underscores the necessity for long-term molecular surveillance, evaluation of vaccine coverage against evolving strains, and enhanced antimicrobial stewardship to strengthen the control efforts for porcine pleuropneumonia in Korea.

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