Longitudinal analysis of serotypes, virulence factors, and MLST profiles of Pasteurella multocida from porcine pneumonia in South Korea (2016–2023)

IMPORTANCE: is a Gram-negative bacterium commonly present in the oropharyngeal microbiota of many animals. In pigs, it contributes to progressive atrophic rhinitis and the porcine respiratory disease complex, both associated with major economic losses. OBJECTIVE: isolates from pigs with respiratory lesions in South Korea (2016-2023), including subspecies identification, capsular serogrouping, virulence gene profiling, and multilocus sequence typing (MLST). METHODS: ) were detected by PCR assays. MLST was conducted using the RIRDC scheme, and phylogenetic analysis of concatenated loci assessed clonal relationships. RESULTS: Serogroup A predominated (109/169, 64.5%), followed by D (47/169, 27.8%) and B (3/169, 1.8%). Serogroups F and A/D were each detected once (0.6%), and 8 isolates were untypable (4.7%). Co-detection of hgbB and pfhA occurred in multiple isolates. Notably, two serogroup B isolates carried both genes, representing the first such finding in Korea and suggesting enhanced virulence potential. MLST identified 5 clonal complexes and 15 sequence types, including ST9 linked to serogroup B. CONCLUSIONS AND RELEVANCE: The emergence of serogroup B/ST9 isolates co-harboring hgbB and pfhA highlights evolving virulence patterns in Korean swine and supports continued molecular and genomic surveillance to guide control strategies and reduce health risks.