Repurposing an ethnomedicinal herb: Horseradish (Armoracia rusticana) as a source of quorum sensing inhibitors to attenuate Pseudomonas aeruginosa virulence.

ETHNOPHARMACOLOGICAL RELEVANCE: Horseradish (Armoracia rusticana P. Gaertn., B. Mey. & Scherb) is a traditional ethnomedicinal herb with established antimicrobial properties, yet its potential to disrupt bacterial communication via quorum sensing inhibition (QSI) remains under-explored.

AIM OF THE STUDY: To evaluate the impact of root processing and extraction methods on the QSI activity of horseradish against a highly recalcitrant multidrug-resistant (MDR) clinical isolate of Pseudomonas aeruginosa.

METHODS

Fresh and dried roots were extracted using five solvent systems. Phytochemical profiles were determined via UHPLC-Q-ToF-MS and QSI activity was validated using Chromobacterium subtsugae CV026, RT-qPCR of QS genes, and fluorescence microscopy for biofilm architecture. Synergistic effects with antibiotics were assessed via checkerboard assays, complemented by in silico molecular docking against LasR, PqsR, and RhlR.

RESULTS

Hexane-ethyl acetate extracts of fresh roots exhibited superior QSI, significantly downregulating core QS (lasR, lasI, rhlR, rhlI, mvfR, pqsH) and virulence (lasB, phzM, rhlC, algK, pvdS) genes. The extract prevented cell adhesion and biofilm maturation while showing strong synergy with meropenem and gentamicin. MS analysis identified isothiocyanates (ITCs), nitriles, and phenolics as key bioactive constituents. Docking revealed that while binding energy correlates with alkyl chain length, functional efficacy results from a multi-component synergy between iberin and other ITCs/nitriles.

CONCLUSION

Horseradish extracts act as potent antivirulence adjuvants, increasing the susceptibility of MDR P. aeruginosa to conventional antibiotics. These findings validate ethnomedicinal use and suggest a low-cost, complementary strategy for managing recalcitrant infections.