Presence of Staphylococcus aureus ST398 and ST9 in Swine in Japan.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is mainly associated with swine and is capable of causing zoonotic infections. The methicillin-resistant S. aureus (MRSA) multilocus sequence type (ST) 398 of swine origin is predominant in Europe and North America, whereas ST9 is predominant in Asia. To evaluate the possible emergence of MRSA in swine, we examined the ST and spa type of 15 methicillin-susceptible S. aureus (MSSA) isolates obtained from swine in 8 different prefectures from north to south Japan between 2003 and 2009. Sequence analyses revealed that 6 porcine MSSA isolates belonged to ST398; 6 to ST9; and 1 each to ST5, ST97, and ST705. Of the 6 MSSA ST398 strains, 4 were classified as spa type t034. This study illustrated that there is a reservoir in Japanese swine of livestock-associated MSSA types.