Inhibition of Fimbria Adhesin Protein of Klebsiella pneumoniae by Using Hylocereus undatus‐Derived Compounds: Insights From Molecular Docking, MD Simulations, and In Vitro Validation

Abstract Klebsiella pneumoniae , a key pathogen causing pneumonia, relies on fimbria adhesin protein to adhere to host tissues, initiating infection and producing virulence factors that damage lung tissue. This study aims to evaluate the inhibitory potential of Hylocereus undatus ‐derived phytochemicals against the fimbria adhesin protein of K. pneumoniae through comprehensive in silico and in vitro analyses. The MD simulations analysis revealed quercetin, 6‐Methyl‐2‐(4‐bromophenyl)‐7‐phenylmethylindolizine, and dasycarpidan‐1‐methanol, acetate exhibited strong binding interaction with the target protein with binding energies of −8.9 kcal/mol, −8.1 kcal/mol, and −7.9 kcal/mol, respectively. These docking results were further validated by cross‐docking, and no significant changes were found in binding energies or the interactions between the ligands and the target protein. Molecular dynamic simulations using YASARA have demonstrated strong stability for all three complexes over 100 ns. ADMET predictions indicated quercetin was non‐toxic. In vitro assays, quercetin exhibited significant inhibitory activity against K. pneumoniae with a zone of inhibition of 24.08 ± 0.60 mm and MIC value of 8.0 ± 0.577 µg/mL. Quercetin, a phytochemical from H. undatus , demonstrated strong binding affinity, stability, and significant in vitro antibacterial activity against K. pneumoniae , highlighting its potential as a novel antimicrobial agent targeting fimbria adhesin proteins.