Four Steroidal Saponins Isolated from the Aerial Parts of <i>Allium jesdianum</i> Exhibit Antibiofilm Effects Against Colistin-Resistant Clinical Strains, with an In Silico Study

Abstract

Background: Global health security is critically threatened by multidrug-resistant Gram-negative bacteria, which frequently overexpress efflux pumps to expel antibiotics, rendering last-resort drugs like colistin ineffective and diminishing treatment options. Methods: This study investigated the antibacterial and antibiofilm potential of four steroidal saponins isolated from the aerial parts of Allium jesdianum Boiss. & Buhse against colistin-resistant strains of Klebsiella pneumoniae, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa. Compounds were extracted, purified using modern chromatographic techniques, and structurally characterized via NMR and mass spectrometry as known saponins, including aginoside and F-gitonin derivatives. Results: Four steroidal-type saponins were isolated. Bioactivity assays revealed that compounds 1 - 3 exhibited minimum inhibitory concentrations (MICs) of 4 mg/mL against colistin-resistant pathogens: Klebsiella pneumoniae, Escherichia coli, and Acinetobacter baumannii, though no bactericidal activity was observed via agar diffusion. Notably, compound 3 demonstrated the strongest antibiofilm activity, achieving up to 75% inhibition at 4 mg/mL. Quantitative real-time PCR analysis showed that all compounds upregulated efflux pump genes (adeB, acrA, blaKPC, oprL), which limit their antibacterial activity. Molecular docking studies further supported the interaction of compound 3 with the adeB efflux pump, indicating strong binding affinity via hydrogen bonding and hydrophobic interactions. Conclusions: These findings highlight the saponin profile in aerial parts of edible plant A. jesdianum as well as their modest antibacterial activity, but with potential as adjuvants in combating biofilm formation.