Emergence of Livestock-Associated Methicillin-Resistant Staphylococcus aureus ST398 in Wild Birds, Brazil

Antimicrobial-resistant and virulent Staphylococcus aureus strains are spreading across diverse environments and hosts, but studies on Brazilian wildlife remain limited. From April to December 2021, oropharyngeal swabs were collected from 197 wild birds spanning five orders, 25 families, and 54 species in São Camilo State Park, a protected Atlantic Forest fragment facing significant pressure from surrounding agricultural landscapes. S. aureus was detected in 12.2% of the birds, including 27 methicillin-susceptible S. aureus (MSSA) and two Methicillin-resistant (MRSA) isolates. MSSA strains showed high inducible Macrolide-Lincosamide-Streptogramin B (MLSB) resistance, with 37% carrying the blaZ gene for penicillin resistance, and antimicrobial-resistant isolates frequently harboring the scn gene. Genomic sequencing identified both MRSA strains as ST398, marking the first report of MRSA ST398 in Brazilian wildlife. These strains displayed a broad resistome, including genes for resistance to multiple antimicrobial classes, as well as a comprehensive virulome, although in vivo assays with Galleria mellonella suggested low virulence. Phylogenomic analysis clustered the MRSA strains with MSSA from swine in northeastern Brazil, suggesting that these strains likely originated in livestock, acquired the SCCmec element, and spread into natural ecosystems. These findings suggest a possible spillover of livestock-associated antimicrobial-resistant S. aureus into a protected forest fragment, highlighting the potential for anthropogenic microbial threats to reach wildlife and underscoring the importance of including wild species in antimicrobial resistance surveillance, especially in fragmented ecosystems increasingly exposed to human activities.