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This study explored the inhibitory effect and mechanism of the culture supernatant of Lactiplantibacillus plantarum HB13-2 on Candida albicans. The minimum inhibitory concentration was determined by the double dilution method. Then, the fluorescent dye calcofluor white (CFW) was used to stain the cell wall and observe it. The results showed that the supernatant enhanced the fluorescence intensity and damaged the cell wall. Flow cytometry and fluorescence microscopy showed that the supernatant changed the membrane permeability of C. albicans. The transmembrane potential was detected using the fluorescent probe DiSC3(5), and it was found that the fluorescence intensity was enhanced, indicating that the supernatant caused dissipation of the transmembrane potential. Through microstructural observation by scanning electron microscopy (SEM), it was found that the supernatant of Lactobacillus plantarum HB13-2 caused cellular deformation and leakage of intracellular contents. As detected by fluorescence staining with 2’,7’-dichlorodihydrofluorescin diacetate (DCFH-DA) and Rhodamine-123, the supernatant resulted in accumulation of a large amount of intracellular reactive oxygen species (ROS) and increased mitochondrial membrane potential. In conclusion, the supernatant of L. plantarum HB13-2 can deform cells by destroying the cell wall and membrane and lead to mitochondrial damage, thereby inhibiting C. albicans. This study will provide a scientific basis for the development of L. plantarum HB13-2 as an oral probiotic.

The purpose of this study is to select lactic acid bacteria with a strong ability to inhibit oral pathogens, high safety and strong oral colonization capacity. Firstly, the strains that could inhibit Streptococcus mutans and Streptococcus gordonii were screened from lactic acid bacteria resource bank in the laboratory by Oxford cup diffusion method. The 28 selected strains were evaluated for hemolytic activity. The results showed that seven of the 28 strains showed α-hemolysis while the remaining 21 did not. The antibacterial metabolites of 16 strains without hemolysis and with a diameter of inhibition zone ≥ 10 mm against S. mutans and S. gordonii were determined by neutralization, catalase and protease susceptibility assays. Then seven strains with strong bacteriostatic capacity and the potential to produce non-organic acid antimicrobial metabolites were selected. The safety evaluation results showed that all seven strains had low acid production ability and caused low corrosion to teeth. The highest tolerable concentration of lysozyme for strain JZ14-1 was 1.6 mg/mL, while that for the other six strains was 1.2 mg/mL, indicating that all seven strains could tolerate lysozyme. Strain HB13-2 was most susceptible to antibiotics. The oral colonization capacity evaluation of strain HB13-2 showed the following results: the highest hydrophobicity of 44.00%, surface acid charge of 20.16%, surface base charge of 49.44%, and content of exopolysaccharides of 0.283 mg/mL. This strain could easily colonize in oral cavity and had low biofilm formation capacity and good self-aggregation capacity, and the maximum inhibition percentage against S. mutans biofilm was 59.72%. Moreover, strain HB13-2 had strong copolymerization capacity with S. mutans, and the copolymerization capacity was 67.40% at 24 h. In conclusion, strain HB13-2 has good antibacterial activity, high safety and strong oral colonization capacity. It is identified as Lactiplantibacillus plantarum by 16S rDNA sequencing.