Shota Fukuda

Periodontal disease is caused by periodontal invasion by pathogens such as Porphyromonas gingivalis. Although recent metagenomic analyses have shown that oral commensal bacteria are abundant in the mouth of healthy individuals, few studies have experimentally verified the benefits and functions of oral commensal bacteria in periodontal diseases. In this study, we focused on Neisseria among the oral commensal bacteria and aimed to experimentally verify its effects on P. gingivalis invasion. We evaluated the inhibitory effect of Neisseria spp. on P. gingivalis invasion using a flow cytometry-based invasion assay and analysed bacterial interactions by visualisation using scanning electron microscopy. Furthermore, we constructed a new experimental pre-mixed culture system that reproduced the interaction environment to evaluate the relevance of this interaction in invasion inhibition. Flow cytometry-based invasion assays showed that all Neisseria spp. inhibited P. gingivalis invasion, with Neisseria mucosa and Neisseria elongata being particularly effective. Interaction analysis using scanning electron microscopy showed that N. mucosa and N. elongata, which have strong inhibitory effects on P. gingivalis invasion, interacted with P. gingivalis at high frequencies. Commensal Neisseria was found to exert a beneficial function by directly interacting with P. gingivalis and inhibiting its invasion of gingival epithelial cells. These results suggest that Neisseria, as a probiotic or synbiotic oral commensal, may represent an innovative approach to preventing periodontal disease.