Isolation, Characterization and Biosafety Evaluation of Lactobacillus Fermentum OK with Potential Oral Probiotic Properties.

It has been reported that certain probiotic bacteria have inhibitory effects against oral pathogens. Lactobacillus spp. have been studied and used as probiotics globally, but due to difficulties with laboratory cultivation and experimentation with oral microorganisms, there are few studies on Lactobacillus spp. isolated from the oral cavity being used against oral pathogens. The purpose of this study was to evaluate the biosafety and inhibitory effects of Lactobacillus fermentum OK as a potential oral biotherapeutic probiotic against oral pathogens. L. fermentum OK was evaluated based on microbial and genetic characteristics. A 5% dilution of L. fermentum OK culture supernatant showed that 60% inhibition against the growth of S. mutans and L. fermentum OK displayed significant inhibitory effects against the growth of Fusobacterium nucleatum, Porphyromonas gingivalis, Streptococcus gordonii, and Streptococcus sanguinis. However, proliferation of L. fermentum OK, when co-cultured with harmful oral bacteria, was retarded. L. fermentum OK was shown to produce 1130 μmol/L hydrogen peroxide, aggregate efficiently with Streptococcus sobrinus, S. gordonii, S. mutans, S. sanguinis, and P. gingivalis, and reduce S. mutans that produced artificial dental plaque by 97.9%. The in vitro cell adhesion capacity of L. fermentum OK to an oral epithelial cell line was 3.1 cells per cell and the cell adhesion of F. nucleatum and S. mutans decreased strongly in protection and displacement assays. L. fermentum OK was evaluated for safety using ammonia production, biogenic amine production, hemolytic property, mucin degradation testing, antibiotic susceptibility, and whole genome sequencing (WGS). Based on this study, L. fermentum OK appears to be a safe and bioactive lactobacterial food ingredient, starter culture, and/or probiotic microorganism for human oral health.