High Prevalence of Clonal Complex 398 Methicillin-Susceptible and -Resistant in Pig Farms: Clonal Lineages, Multiple Drug Resistance, and Occurrence of the Staphylococcal Cassette Chromosome IX.

High prevalence of livestock-associated methicillin-susceptible and -resistant (LA-MSSA and LA-MRSA, respectively) in livestock farms, particularly pig farms, is an increasingly serious threat to food safety and public health. In this study, 173 (84 MRSA and 89 MSSA) isolates from healthy pigs, farm environments, and farm workers in Korea were examined to determine the (1) genetic diversity of isolates (sequence type [ST], , and types), (2) staphylococcal cassette chromosome (SCC) types of MRSA isolates, and (3) multidrug resistance (MDR) phenotypes of MRSA and MSSA isolates. Clonal complex 398 (CC398) genotypes of MRSA and MSSA isolates, particularly CC398- type t571- I lineages, displaying MDR phenotypes were highly prevalent in pig farms. High prevalence of CC398-t571 MRSA and MSSA was more frequently associated with weaning piglets and growing pigs. Moreover, the same clonal lineages of isolates colonized both pigs and farm workers, suggesting the transmission of antimicrobial-resistant CC398 MRSA and MSSA between pigs and humans in the pig farms. Furthermore, two dominant SCC types, SCC V and SCC IX, were identified in CC398 MRSA isolates colonizing healthy pigs. To the best of our knowledge, this is the first report of a CC398 LA-MRSA isolate carrying SCC IX in Korea. Collectively, these results suggest widespread distribution of the CC398 lineage among MRSA and MSSA isolates in pigs, farm environments, and farm workers in Korea.