Genetic diversity and virulence profiling of Streptococcus suis isolates from swine lesions in South Korea: a longitudinal study

Importance: Streptococcus suis is a zoonotic pathogen that poses a threat to human and animal health. In pigs, it causes arthritis, meningitis, and septicemia, while in humans it leads to meningitis, endocarditis, pneumonia, septicemia, and septic shock. Effective control of this pathogen is important for both public and animal health. Objective: This study characterized S. suis isolates from swine lesions in the Republic of Korea to provide insights into their epidemiological features. Methods: Seventy-four isolates were collected from diverse tissues. Serotypes were determined using multiplex PCR targeting capsular polysaccharide genes, and multi-locus sequence typing (MLST) was conducted with seven housekeeping genes. The virulence-associated genes epf, mrp, and sly were screened by multiplex PCR. Results: Sixteen serotypes were identified, with serotype 2 most prevalent (27.0%), followed by serotypes 3, 8, 7, 13, and 4. MLST revealed 41 sequence types, including 26 novel STs. Among virulence genes, sly was most frequently detected, but nearly half of the isolates were negative for all three genes. The serotype and sequence type distribution also showed notable year-to-year variations, indicating ongoing genetic diversification in Korea. Conclusions and Relevance: These findings underscore the need for continuous surveillance to track serotype shifts and the emergence of novel lineages. Molecular tools such as MLST and virulence gene profiling enhance epidemiological understanding and support risk assessment for this zoonotic bacterium.