AimsTo evaluate the inhibitory activity of probiotics against oral Candida species. Methods and ResultsFour commercial probiotic products were screened. Bacillus subtilis R0179 was found to have a significant antifungal effect. Bacillus subtilis-Candida interactions were evaluated using disc diffusion tests, confocal laser scanning microscopy, scanning electron microscopy and interaction with engineered human oral mucosa tissue. Bacillus subtilis exhibited clear zones of inhibition for Candida albicans and Candida parapsilosis but not for Candida krusei. A remarkable reduction in the number of Candida cells and abundant Candida cell death were visualized with confocal laser scanning microscopy. Shrinkage and deformation of Candida cells was observed using scanning electron microscopy. Culture of C.albicans on engineered human oral mucosa tissues resulted in the presence of a large number of yeast cells on the tissue surface and the development of large-scale tissue damage. However, comparatively fewer Candida cells were observed on B.subtilis-treated tissues. We also use ultra performance liquid chromatography/time of flight mass spectrometry (UPLC/TOF MS) to explore the preliminary antifungal mechanism of B.subtilis R0179 and to detect that whether it can secrete an antifungal agent, Iturin A. ConclusionsBacillus subtilis R0179 exhibits a significant inhibitory effect on the growth of Candida species. Significance and Impact of the StudyBacillus subtilis has the potential to be used in the prevention or treatment of oral candidiasis.