Novel biosurfactant-stabilized nanoemulsions integrating interfacial stabilization and antibacterial activity for safe surface disinfection.

Chemical disinfectants are widely used for microbial control. However, concerns regarding their safety and environmental impact have driven the development of alternative antimicrobial systems based on natural components. Here, a biosurfactant (BS) derived from Bacillus velezensis GJ1 was used to construct a natural grade nanoemulsion (NE) system using thyme oil as the oil phase. Unlike conventional formulations in which surfactants mainly act as passive stabilizers, BS in this system contributed to both interfacial stabilization and antibacterial activity, enabling the development of a natural-grade NE system with combined physicochemical and antibacterial functionalities. The resulting NEs exhibited stable physicochemical properties and consistent droplet characteristics. Antibacterial evaluation demonstrated strong activity against Listeria monocytogenes and Escherichia coli O157, with comparable efficacy across different co-surfactant systems. This suggests that BS may contribute to the antibacterial performance of the NE systems. Microscopic analyses confirmed the membrane disruption and increased permeability of the bacterial cells. Under contact surface conditions, the BS-containing NEs exhibited measurable antibacterial activity against both L. monocytogenes and E. coli O157 under the tested conditions. NEs exhibited low cytotoxicity, minimal skin irritation, and negligible phytotoxicity at antibacterial concentrations. The findings suggest the potential applicability of BS-stabilized NEs as natural antimicrobial systems in which the surfactant contributes to both interfacial stabilization and antibacterial activity. These results may provide useful insights for the development of effective and safer disinfectant formulations based on naturally derived components.