Molecular characterization and clonal genetic diversity of methicillin-resistant Staphylococcus aureus of pig origin in Taiwan

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is an emerging public health threat. The aims of this study were to identify nasal carriage of MRSA in finishing pigs from different geographical areas of Taiwan and to compare the genetic features of LA-MRSA with other countries. A total of 299 swine nasal samples were collected from 11 counties in western Taiwan with 220 identified MRSA isolates characterized by spa, SCCmec, MLST, pulsed-field gel electrophoresis (PFGE), antibiogram, and Panton-Valentine leukocidin (PVL) toxin genes. A widespread LA-MRSA clone, ST9-t899-PVL-negative, was detected as the predominant (91.6%) clone in Taiwan pigs, and a novel spa type t7616 was identified. Most isolates carried SCCmec type V but lacked ccrC gene (98.8%), a particular feature that was observed for the first time. The integration of minimum spanning trees (MST) based on a PFGE distance matrix and geographical information showed high genetic diversity among ST9-t899 isolates with three unique subpopulations identified in two counties that are nearby each other. Multidrug resistance (MDR) was prevalent in isolates from different counties with more than 80% resistance to erythromycin, ciprofloxacin, gentamicin, tetracycline, and clindamycin. In conclusion, this study reported the first identified LA-MRSA clone of MDR-ST9-t899-V lacking ccrC dominant in pig farms in western Taiwan that differed from ST398 in Europe and North America. Close monitoring of this MDR unique clone is warranted to survey its spread from livestock to humans.