Optimized niosomal nanocarriers for nisin encapsulation and prolonged antibacterial activity

This study systematically optimized nisin-loaded niosomes prepared by thin-film hydration using Span 60 and Tween 80 (2:1 molar ratio) with cholesterol. Thirteen formulation conditions were screened using hydration pH, surfactant-to-cholesterol ratio (ST: Ch), and wall-to-core ratio as formulation variables. The optimized formulation (pH 7.4, ST: Ch 50:50, wall-to-core 3:1) showed an encapsulation efficiency of 67.7 ± 1.9%, loading capacity of 16.9 ± 0.9%, particle size of 383.3 nm, PDI of 0.283, and zeta potential of -8.6 ± 0.7 mV. FTIR analysis showed retention and changes in characteristic bands of nisin and the niosomal components, while DSC demonstrated changes in phase transition behavior after nisin incorporation. TEM and AFM showed predominantly spherical vesicles. In time-kill assays, the complete nisin-loaded niosomal formulation, tested as prepared, was compared with free nisin at equal nominal concentrations. Free nisin showed the lower MIC, its distinguishing feature was a prolonged antibacterial effect over 24–72 h, with an MBC of 50 µg mL⁻¹ versus 100 µg mL⁻¹ for Staphylococcus aureus and 200 µg mL⁻¹ versus > 200 µg mL⁻¹ for Escherichia coli. During 40 days of storage at 4 °C, particle size increased by 18.2% and EE decreased by 26.4% relative to day 1. These results demonstrate that nisin can be efficiently incorporated into niosomes under neutral hydration conditions and that the formulation maintains antibacterial activity over prolonged incubation, consistent with the rationale of encapsulation as a means of protecting nisin and extending its activity over time.