Molecular and functional characterization of Streptococcus dentisani 7746: gene expression, biofilm modulation and immunoregulatory effects under cariogenic conditions

Background Streptococcus dentisani has emerged as a promising oral probiotic due to its inhibitory capacity against cariogenic species and its potential to modulate host immune responses. However, the molecular and functional basis of its ecological role within oral biofilms remains poorly defined. Methods: We performed a molecular characterization of S. dentisani 7746 by assessing gene expression under varying glucose concentrations and evaluating its impact on mixed-species biofilms and epithelial cell responses. Semi-quantitative RT-PCR and CFU enumeration assays were conducted to quantify gene expression and bacterial abundance, respectively. Results: Adhesion-related genes (fap1, cshA) and immunomodulatory genes (ppiA, atlA) showed stable expression with no consistent glucose-dependent regulation, except for ppiA, which was significantly downregulated at high glucose. In contrast, pox—a gene encoding pyruvate oxidase—was repressed under glucose-rich conditions, suggesting a regulatory link between carbohydrate availability and hydrogen peroxide production. Functionally, S. dentisani reduced S. mutans abundance and promoted Lactobacillus persistence in mixed biofilms. Moreover, pre-exposure to S. dentisani altered pathogen internalization and cytokine responses in HeLa cells, favoring anti-inflammatory signaling. Conclusion: Our findings reveal that S. dentisani maintains a stable molecular profile under cariogenic stress and exerts multifaceted ecological functions—competitive, cooperative, and immunomodulatory—that support its probiotic potential. These results encourage further in vivo investigations to validate its clinical applications.