Chitosan-sodium dodecyl sulfate nanoparticles: a promising approach for enhancing antibacterial activity against Streptococcus mutans of grapefruit seed extract

In this study, grapefruit seed extract (GSE)-loaded nanoparticles (GNPs) were formed through ionic gelation between chitosan (CS) and sodium dodecyl sulfate (SDS) to improve antibacterial activity against oral bacteria, such as Streptococcus mutans, and to demonstrate the impact of particle size on antimicrobial activity. Particle size was negatively correlated with the antibacterial effect; the smaller GNPs showed significantly higher antimicrobial activity than the other particles. The optimal formulation of the smaller GNPs was determined using response surface methodology (RSM). The optimized GNPs improved antibacterial activity, which was approximately 3.5 times higher than that of free GSE (p < 0.05). Moreover, the GNPs were effective at reducing bacterial growth, achieving a reduction of more than 3 log₁₀ CFU/mL within the first 3 h and complete inhibition of bacterial growth after 9 h. This study suggests that nanoencapsulation significantly enhances its antibacterial activity against oral bacteria.