Novel Variants of SCC Type IX Identified in Clonal Complex 398 Livestock-Associated Methicillin-Resistant from Pork Production Systems in Korea.

: The occurrence of novel variants of staphylococcal cassette chromosome (SCC) in livestock-associated methicillin-resistant (LA-MRSA) has frequently been reported, posing significant zoonotic concern worldwide. In this study, the occurrence of novel types of SCC IX elements was identified in two clonal complex (CC) 398 LA-MRSA strains derived from a pig farm and a slaughterhouse in Korea. : Whole-genome sequence analysis of the two CC398 MRSA-SCC IX strains, designated KF1A-1172 and JS1E-122, revealed that these strains are most closely related to previously characterized strains of CC398 LA-MRSA carrying SCC V isolated from pig farms in Korea. : Further structural analysis of the SCC IX in KF1A-1172 and JS1E-122 revealed the presence of multiple gene complexes (, and a truncated ), including genes for SCC type IX. In addition, the pseudo-SCC (ΨSCC) elements, genes associated with the type 1 restriction-modification (RM) system, and zinc resistance gene , were identified in the SCC IX. : These findings suggest that the multiple recombination events of elements derived from various SCC types contributed to the emergence of the novel SCC IX variant. The identification of these novel SCC IX types in CC398 LA-MRSA also suggests that epidemiological diversification of SCC IX in CC398 LA-MRSA is an ongoing event, necessitating continued surveillance on the emergence of novel SCC variants. This study is the first to report the complete genome sequences of CC398 MRSA carrying SCC IX in Korea.