Structure-based drug discovery targeting <i>fmhA</i> in <i>Staphylococcus warneri</i> using extracts of <i>Calliandra harrisii</i> : an integrated ethnobotanical and <i>in silico</i> approach

<i>Staphylococcus warneri</i> is a Gram-positive bacterium increasingly associated with urinary tract and skin infections and shows emerging multidrug resistance. In this study, <i>S. warneri</i> was cultured, and the virulence-associated <i>fmhA</i> gene was amplified, sequenced, and submitted to GenBank, representing the first reported molecular characterization of <i>fmhA</i> in this species. An ethnobotanical approach guided the selection of <i>Calliandra harrisii</i> for antimicrobial evaluation. Methanolic Soxhlet extraction followed by GC-MS analysis identified multiple bioactive phytochemicals. The three-dimensional structure of the Aminoacyl-transferase FemA (<i>fmhA</i>) protein was modeled and validated, showing acceptable structural quality. Selected phytochemicals were screened using ADME criteria, molecular docking, and molecular dynamics simulations. Among them, spiro[1,3-dioxolane-2,2'-[6,7] diazabicyclo[3.2.2] non-6-ene] demonstrated favorable binding affinity, structural stability during 100 ns simulations, and energetically favorable MM/GBSA and MM/PBSA profiles. Density functional theory analysis revealed a moderate HOMO-LUMO gap, supporting balanced chemical reactivity and stability. Pharmacophore modeling and <i>in silico</i> toxicity prediction further suggested acceptable drug-likeness and low oral toxicity. Collectively, this integrated ethnobotanical and <i>in silico</i> framework identifies <i>C. harrisii</i> as a promising source of antibacterial agents and highlights spiro[1,3-dioxolane-2,2'-[6,7]diazabicyclo[3.2.2] non-6-ene] as a potential lead compound targeting <i>fmhA</i> in <i>S. warneri</i>. Experimental validation is warranted to confirm its therapeutic potential.