Molecular Characterization and Antimicrobial Resistance of Livestock-Associated Methicillin-Resistant <i>Staphylococcus aureus</i> Isolates from Pigs and Swine Workers in Central Thailand

Abstract

This study presents molecular characteristics of livestock-associated methicillin-resistant <i>Staphylococcus aureus</i> (LA-MRSA) from pigs and swine workers in central Thailand. Sixty-three MRSA isolates were recovered from pigs (<i>n</i> = 60) and humans (<i>n</i> = 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 <i>spa</i> type t034 (<i>n</i> = 55). ST9 and ST4576 had t337 (<i>n</i> = 8) and carried staphylococcal cassette chromosome <i>mec</i> (SCC<i>mec</i>) IX only. MRSA-ST398-t034 contained various SCC<i>mec</i>, including SCC<i>mec</i> V (<i>n</i> = 42), a novel SCC<i>mec</i> composite island (<i>n</i> = 12), and a nontypeable SCC<i>mec</i> (<i>n</i> = 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 <i>cfr</i> 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.