Inhibition of Streptococcus Biofilm Formation by 6′-Sialyllactose and N-Acetylneuraminic Acid

Background/Objectives: Oral hygiene is crucial for maintaining overall health, as poor oral care can lead to various systemic diseases. Although xylitol is widely used to inhibit plaque formation, more effective agents are needed to control oral biofilms. Herein, we evaluated the inhibitory effects of sialyllactose (SL), a type of human milk oligosaccharide (HMO), and its partial structure N-acetylneuraminic acid (Neu5Ac) against Streptococcus biofilm. Methods: Under a CO2 atmosphere, Streptococcus mutans and mixed Streptococcus species were each cultivated in vitro, and the inhibitory effects of HMOs [2′-fucosyllactose, 3′-sialyllactose (3′-SL) and 6′-sialyllactose (6′-SL)] and Neu5Ac on biofilm formation were evaluated. Bacterial biofilm formation was quantified using the crystal violet assay. Biofilm architecture and viability were visualized using confocal laser-scanning microscopy (CLSM) with SYTO9/propidium iodide staining. Transcriptomic responses of S. mutans biofilms to the test compounds were analyzed by RNA-Seq. Statistical analysis was performed using one-way analysis of variance followed by Tukey’s test. Results: SLs and Neu5Ac at 100 mM significantly inhibited S. muta