Natural long-chain fatty acyl solamines from the leaves of Solanum bulbocastanum Dun. show antiseptic properties

Long-chain fatty acyl solamines, recently identified in the leaves of Solanum bulbocastanum Dun., have been shown to confer resistance against plant pests such as the Colorado potato beetle and the phytopathogenic oomycete Phytophthora infestans (Mont.) de Bary. Owing to their structural resemblance to the antiseptic cetylpyridinium chloride, this study aimed to evaluate a fraction of a methanolic S. bulbucastanum leaf extract mainly containing long-chain fatty acyl solamines for potential antiseptic applications. Minimal inhibitory concentrations (MICs) were determined against eight clinically relevant human pathogens, and minimal bactericidal concentrations (MBCs) were assessed for two model bacteria. Atomic force microscopy and lactate dehydrogenase (LDH) release assays were employed to investigate the mechanism of action. Cytotoxicity was evaluated on normal human dermal fibroblasts and Vero E6 cells using MTT and LDH assays, as well as real-time cell analysis and live-cell imaging. The fraction exhibited antimicrobial activity against all tested pathogens (MICs of 128–256 μg/mL for the majority of the pathogens) and demonstrated bactericidal properties (MBCs of 256 μg/mL), likely mediated by nonspecific membrane disruption. In mammalian cell assays, the fraction mirrored the cytotoxic effect of cetylpyridinium chloride in MTT assay (Fibroblasts: IC₅₀ = 1.2 μg/mL, Vero E6: IC₅₀ = 2.2 μg/mL) and the profile in real time cell analysis, suggesting a comparable mode of action. These findings highlight long-chain fatty acyl solamines as promising candidates for the development as bio-based antiseptics, offering a potential green alternative to conventional agents.