Prevalence and Characteristics of Methicillin-Resistant Staphylococcus aureus Isolates in Pigs and Pig Farmers in Korea

In this study, we investigated the prevalence and characteristics of methicillin-resistant Staphylococcus aureus (MRSA) isolates from pigs and pig farmers in Korea. A total of 1245 nasal swabs were collected from pigs and farmers at 53 pig farms in nine provinces from 2012 to 2016. The prevalence of MRSA was 7.9% (88/1119) in pigs and 16.7% (21/126) in farmers. Among 119 farmers working on conventional farms, 21 (17.6%) tested positive for MRSA. However, no MRSA was detected in either pigs or farmers at four organic farms. The individual pig-level prevalence of MRSA differed between age groups, with the percentage of positive samples being highest in weaners (17.3%), followed by growers (9.0%), piglets (6.5%), finishers (4.4%), and sows (0%). Two different lineages of MRSA were detected among the 109 isolates from pigs and farmers: (1) livestock-associated types of MRSA belonging to 27 isolates of ST541-t034-V, 24 isolates of ST398-t571-V, 17 isolates of ST398-t034 variant (G420A)-V, and one isolate of ST541-t8588-V; and (2) community-associated types of MRSA belonging to 21 isolates of ST188-t189-IV, 14 isolates of ST72-t324-IV, three isolates of ST72-t664-IV, one isolate of ST72-t148-IV, and one isolate of ST72-t5440-IV. Identical genotypes were detected in both pigs and farmers at six farms. New MRSA clones were isolated from pigs (ST398-t034 (G420A)-V, ST188-t189-IV, and ST398-t571-V) and pig farmers (ST541-t8588-V and ST72-t5440-IV). The prevalence of MRSA was also correlated with antibiotic usage, and the clones showed diversification between pigs and farmers. Ultimately, the increased frequency and diversification of livestock-associated MRSA could be a potential threat to public health in Korea. To our knowledge, this is the first study to report the prevalence and characteristics of MRSA in pigs and pig farmers in Korea.