Molecular Characterization and Antimicrobial Resistance of Livestock-Associated Methicillin-Resistant Isolates from Pigs and Swine Workers in Central Thailand.

This study presents molecular characteristics of livestock-associated methicillin-resistant (LA-MRSA) from pigs and swine workers in central Thailand. Sixty-three MRSA isolates were recovered from pigs ( = 60) and humans ( = 3). Two major LA-MRSA lineages, including sequence type (ST) 398 and clonal complex 9 (ST9 and ST4576, a novel single-locus variant of ST9), were identified. ST398 had type t034 ( = 55). ST9 and ST4576 had t337 ( = 8) and carried staphylococcal cassette chromosome (SCC) IX only. MRSA-ST398-t034 contained various SCC, including SCC V ( = 42), a novel SCC composite island ( = 12), and a nontypeable SCC ( = 1). All isolates were multidrug resistant and carried common resistance genes found in LA-MRSA. This is the first report of the presence of swine MRSA ST398 and multidrug resistance gene in MRSA ST9 in Thailand. With identical molecular characteristics, pigs could be a source of MRSA ST398 spread to humans. A minor variation of genetic features and resistance gene carriage in both lineages represented a heterogeneous population and evolution of the endemic clones. A monitoring program and farm management, with prudent antimicrobial uses, should be implemented to reduce spreading. Strict hygiene and personal protection are also necessary to prevent transfer of LA-MRSA to humans.