In Silico-Guided Discovery and In Vitro Evaluation of Natural Sortase A Inhibitors to Fight Multidrug-Resistant Staphylococcus aureus

Antimicrobial resistance poses a serious global health threat. Sortase A (SrtA), a membrane-bound cysteine transpeptidase responsible for anchoring key virulence factors to cell wall of Gram-positive bacteria, acts as critical driver of pathogenicity. Here, molecular dynamics simulations were employed to explore SrtA conformational flexibility and guide a structure-based virtual screening of approximately 300,000 natural compounds. Seven structurally diverse hits were selected based on their ability to bind the multiple conformations and their favorable docking scores. Drug-likeness and pharmacokinetic properties were predicted and compared with those of agents currently used against multidrug-resistant Staphylococcus aureus, revealing that the identified compounds obey both Lipinski's and Muegge's rules. In vitro assays confirmed the SrtA inhibitory activity of the two compounds in the low micromolar range. Noteworthy, both compounds significantly reduced S. aureus adhesion to fibrinogen, suggesting functional inhibition of endogenous bacterial SrtA. These findings support the potential of these natural scaffolds as antivirulence drug candidates.