Targeting methicillin-resistant <i>Staphylococcus aureus</i> : The comprehensive action of ent-kaurane diterpenoids on bacterial integrity

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) represents a considerable challenge to global health owing to its resistance to antibiotics. In our prior research, we identified four ent-kaurane diterpenoids (compounds <b>1-4</b>) isolated from <i>Siegesbeckia orientalis</i> L., which exhibited anti-MRSA activity. Nevertheless, the precise mechanisms by which these compounds exert their effects remain to be fully elucidated. This study aims to comprehensively evaluate the anti-MRSA properties and explore the biological processes associated with the activity of compounds <b>1-4</b>. We utilized the minimum broth dilution method, electron microscopy, and membrane integrity assays to demonstrate that these compounds inhibit the growth of MRSA by disrupting cell wall and membrane structures. Additionally, crystal violet staining confirmed their efficacy in disrupting mature biofilms. In a murine model of bacteremia, the tested compounds <b>1-4</b> demonstrated a reduction in septic symptoms and exhibited favorable biosafety profiles, with compound <b>1</b> showing the most significant antibacterial effects. Transcriptomic analysis indicated that compound <b>1</b> disrupts peptidoglycan synthesis and interferes with the metabolism of cell wall precursors. Furthermore, it modulates the expression of genes associated with ion transport and membrane-related metabolic enzymes, thereby compromising the integrity of both the cell wall and the cytoplasmic membrane. In conclusion, this study systematically characterizes the anti-MRSA activity of the diterpenoid components derived from S. <i>orientalis</i> and identifies key biological processes and gene expression changes linked to their effects, and presents a promising new strategy for the development of natural anti-MRSA pharmaceuticals.