Molecular types, genetic characteristics and phylogenomic analysis of Staphylococcus aureus causing infective endocarditis

Introduction: Staphylococcus aureus is a leading cause of infective endocarditis (IE), yet its molecular epidemiology remains understudied. In this study, genomic data from 285 IE-associated S. aureus strains wre analyzed to inform clinical strategies. Methodology: Strains were characterized by multilocus sequence typing (MLST), spa typing, and SCCmec classification. Antibiotic resistance genes (ARGs) and virulence factors (VFs) were identified from genomic data, and phylogenetic trees were constructed. Results: Predominant sequence types (STs) included ST45 (CC45), ST5 (CC5), ST8 (CC8), ST15 (CC15), ST30 (CC30), ST1 (CC1), and ST188 (CC1). Common spa types were t2, t8, t230, and t88. Among 46 mecA-positive strains, SCCmec IV (50%) and II (34.8%) predominated. MecA was more prevalent in ST5 and ST8 strains but less prevalent in ST45 and ST15 strains. ST45 strains lacked splA, splB, and splE, unlike other STs. ST45 and ST8 strains harbored higher numbers of ARGs, while ST15 and ST188 carried fewer ARGs. Similarly, ST5 and ST1 strains exhibited higher VF counts than ST15 and ST188 strains. Phylogenetic tree revealed that some clades dominated by a single ST contained insertions of strains from different STs, and closely related strains were primarily associated with different CC groups. Some CC1 and CC8 strains clustered together on a branch, indicating a close genetic relationship. Conclusions: ST5 and ST8 clones pose high ARG or VF risks and warrant targeted therapy, whereas ST15 and ST188 may represent lower-risk lineages. The prevalence of SCCmec IV highlights the contribution of community-associated MRSA to IE. Phylogenetic inconsistencies reflect adaptive evolution of S. aureus in IE.