Interactions between Streptococcus oralis, Actinomyces oris, and Candida albicans in the development of multispecies oral microbial biofilms on salivary pellicle

The fungus Candida albicans is carried orally and causes a range of superficial infections that may become systemic. Oral bacteria Actinomyces oris and Streptococcus oralis are abundant in early dental plaque and on oral mucosa. The aims of this study were to determine the mechanisms by which S. oralis and A. oris interact with each other and with C. albicans in biofilm development. Spatial distribution of microorganisms was visualized by confocal laser scanning microscopy of biofilms labeled by differential fluorescence or by fluorescence in situ hybridization (FISH). Actinomyces oris and S. oralis formed robust dual-species biofilms, or three-species biofilms with C. albicans. The bacterial components tended to dominate the lower levels of the biofilms while C. albicans occupied the upper levels. Non-fimbriated A. oris was compromised in biofilm formation in the absence or presence of streptococci, but was incorporated into upper biofilm layers through binding to C. albicans. Biofilm growth and hyphal filament production by C. albicans was enhanced by S. oralis. It is suggested that the interkingdom biofilms are metabolically coordinated to house all three components, and this study demonstrates that adhesive interactions between them determine spatial distribution and biofilm architecture. The physical and chemical communication processes occurring in these communities potentially augment C. albicans persistence at multiple oral cavity sites.