Aqueous extract of Nasturtium officinale: a potential therapeutic approach to be explored in the fight against multidrug-resistant Pseudomonas aeruginosa

The rise in global bacterial resistance has made the development of new therapies an urgent challenge, positioning Pseudomonas aeruginosa as a critical priority pathogen. In this context, phytotherapy stands out due to the wide diversity of bioactive compounds with antimicrobial potential. Thus, the present study evaluated the antibacterial and antibiofilm efficacy of an aqueous watercress ( Nasturtium officinale ) extract against eight P. aeruginosa strains (one ATCC standard strain and seven multidrug-resistant clinical isolates), in addition to assessing its cytotoxicity in human keratinocytes (HaCat). The extract was phytochemically characterized by MALDI-TOF. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by microdilution using the M7-A9 protocol (CLSI). Activity against 48-hour-old mature biofilms (at concentrations of 50, 100, and 200 mg/mL) and cell viability in HaCat cells were measured using the MTT colorimetric assay. Phytochemical analysis revealed the predominant presence of glucosinolates (gluconasturtiin and phenethyl isothiocyanate) and flavonoids. MIC and MBC values ranged from 12.5 mg/mL to 50 mg/mL. In the biofilm model, the extract significantly reduced bacterial metabolic viability in all strains, surpassing the efficacy of the antiseptic chlorhexidine (CHX) in the wild-type isolates (S2, S3, and S5). In cytotoxicity assays, the 50 mg/mL concentration proved to be biocompatible, maintaining keratinocyte viability above 90%. Thus, the aqueous extract of N. officinale demonstrated promising antimicrobial activity against planktonic strains and biofilms of multidrug-resistant P. aeruginosa . The 50 mg/mL concentration establishes a safe and effective therapeutic window in vitro, paving the way for future in vivo trials.