Effect of L. plantarum on Caries Prevention and the Oral–Gut Microbiome In Vivo

While Lactiplantibacillus plantarum has shown promise against cariogenic pathogens, its in vivo effects on caries prevention remain unexplored. This study used a rat model to investigate the effect of L. plantarum early-life oral inoculation on oral and gut microbiomes, host immune responses, and serum metabolites. Forty 14-day Sprague–Dawley rat pups were randomly allocated into 5 groups: (1) blank control, (2) L. plantarum colonization alone, (3) Streptococcus mutans and Candida albicans co-colonization, (4) L. plantarum precolonization before S. mutans and C. albicans exposure, and (5) 2-wk treatment of L. plantarum after S. mutans and C. albicans exposure. Dynamic colonization of L. plantarum, S. mutans, and C. albicans in saliva and plaque was assessed using a culture-dependent method. Saliva, plaque, and fecal microbiomes were assessed using 16S ribosomal RNA gene sequencing. Caries scoring was performed using Keyes’ scoring system and microcomputed tomography. Serum metabolite and immune markers were assessed through liquid chromatography tandem mass spectrometry untargeted metabolomics and multiplex immune profiling. We found that 3-d L. plantarum inoculation established stable L. plantarum colonization in the oral cavity of young rats. Inoculation timing of L. plantarum was critical for caries prevention. L. plantarum precolonization significantly reduced caries lesions compared with the S. mutans and C. albicans group, whereas 2 wk of postexposure treatment did not demonstrate a protective effect. L. plantarum precolonization led to distinct microbial shifts in saliva, plaque, and gut microbiomes, with an increased abundance of beneficial bacteria, such as Streptococcus azizii, Bifidobacterium animalis, Faecalibaculum rodentium, and Allobaculum stercoricanis, and a decrease in S. mutans. L. plantarum preinoculation also influenced metabolic profiles, with 1 metabolite upregulated and 24 downregulated, although immune marker differences were minimal. In conclusion, L. plantarum oral colonization before host exposure to oral cariogenic pathogens effectively reduced caries and modulated the profile of oral and gut microbiomes and serum metabolic profile.