Nisin-loaded chitosan/sodium alginate microspheres enhance the antimicrobial efficacy of nisin against Staphylococcus aureus.

Aims: To develop and evaluate nisin-loaded chitosan/sodium alginate (CS/SA) microspheres as an improved antimicrobial delivery system targeting Staphylococcus aureus strains.

Methods and results: The microspheres were prepared using a modified water-in-oil emulsion cross-linking method, resulting in spherical particles sized 1-8 µm with a surface charge of -7.92 ± 5.09 mV, confirmed by scanning electron microscopy (SEM) and Zetasizer analysis. Encapsulation efficiency (EE) and loading capacity (LC) of nisin were 87.60% ± 0.43% and 1.99% ± 0.01%, respectively. In vitro release studies over 48 h indicated a controlled release pattern of nisin, described by the Korsmeyer-Peppas model, with higher release rates at 37°C and alkaline pH. Antimicrobial assays showed an enhanced efficacy of nisin-loaded CS/SA microspheres compared to free nisin, with minimum inhibitory concentration values reduced by 50%. Confocal laser scanning microscopy (CLSM), SEM, and transmission electron microscopy showed significant bacterial membrane damage and cellular disruption induced by the microspheres.

Conclusions: This study highlights the potential of nisin-loaded CS/SA microspheres as an innovative antimicrobial delivery system with improved stability and antimicrobial efficacy against S. aureus, addressing limitations associated with nisin applied alone.