Emergence of Cfr -Mediated Linezolid Resistance among Livestock-Associated Methicillin-Resistant Staphylococcus aureus (LA-MRSA) from Healthy Pigs in Portugal.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) ST398 is mainly found in Europe and North America, colonizing the nasal cavity of pigs. This study characterized the MRSA isolates recovered from pig nasal swabs ( n = 171) by evaluating the antimicrobial susceptibility profile by broth microdilution and characterizing the genetic lineages by spa -typing. Three linezolid-resistant isolates were subjected to Whole-Genome Sequencing (WGS). All strains harbored the mecA gene and were resistant to tetracycline and susceptible to vancomycin. A high frequency of multidrug resistance (97.6%) was evidenced, with 55 different multidrug resistance profiles identified. The MRSA strains were found to belong to 17 spa -types, three being novel. The linezolid-resistant strains appeared to belong to the ST398 type, spa -type t011, and SCC mec _type_Vc and to harbor the cfr , fex A, bla Z, mec A, tet M, and tet K genes. The cfr gene was predicted to be carried in the plasmid, flanked by IS Sau9 and the transposon TnpR. MRSA from Portuguese fattening pigs present a high diversity of genetic lineages. The presence of cfr -positive LA-MRSA may represent a risk of transmission to humans, mainly to those in contact with livestock.