N-nonyloxypentyl-L-deoxynojirimycin reduces Stenotrophomonas maltophilia virulence in vitro and in Galleria mellonella infection model

Introduction – Stenotrophomonas maltophilia is an opportunistic pathogen able to resist multiple classes of antibiotics and form robust biofilms, making it difficult to treat. Methods – The antimicrobial and anti-virulence activity of the iminosugar N-nonyloxypentyl-L-deoxynojirimycin (L-NPDNJ) against S. maltophilia was evaluated by in vitro and in vivo models. Results and discussion – L-NPDNJ exhibited weak bactericidal activity but showed additive effects when used in combination with amikacin and tobramycin, reducing their minimum inhibitory concentrations by two- to threefold. At sub-inhibitory concentrations, L-NPDNJ was found to significantly modulate the expression of genes involved in antibiotic resistance, biofilm regulation, and virulence, including those encoding efflux pumps, global regulators, and extracellular proteases. These transcriptional changes were found to be associated with significant phenotypic effects. At sub-inhibitory concentrations, L-NPDNJ reduced cell surface hydrophobicity by up to 90%, impaired adhesion to abiotic surfaces and to human lung epithelial cells by over 90%, and disrupted preformed biofilms, decreasing biofilm biomass and metabolic activity by approximately 70%. In addition, L-NPDNJ has been shown to enhance macrophage phagocytosis and reduce intracellular bacterial survival, while improving epithelial cell viability. Notably, pretreatment of S. maltophilia cells with L-NPDNJ led to a substantial reduction in bacterial virulence in the Galleria mellonella infection model in a dose-dependent manner. Conclusion – Collectively, these findings demonstrate that L-NPDNJ exerts a broad anti-virulence effect against S. maltophilia and suggest its potential application as an adjuvant strategy to improve the treatment of infections caused by this multidrug-resistant pathogen.