Streptococcus oralis maintains homeostasis in oral biofilms by antagonizing the cariogenic pathogen Streptococcus mutans

Abstract

Bacteria residing in oral biofilms live in a state of dynamic equilibrium with one another. The intricate synergistic or antagonistic interactions between them are crucial for determining this balance. Using the six-species Zürich "supragingival" biofilm model, this study aimed to investigate interactions regarding growth and localization of the constituent species. As control, an inoculum containing all six strains was used, whereas in each of the further five inocula one of the bacterial species was alternately absent, and in the last, both streptococci were absent. Biofilms were grown anaerobically on hydroxyapatite disks, and after 64 h they were harvested and quantified by culture analyses. For visualization, fluorescence in situ hybridization and confocal laser scanning microscopy were used. Compared with the control, no statistically significant difference of total colony-forming units was observed in the absence of any of the biofilm species, except for Fusobacterium nucleatum, whose absence caused a significant decrease in total bacterial numbers. Absence of Streptococcus oralis resulted in a significant decrease in Actinomyces oris, and increase in Streptococcus mutans (P < .001). Absence of A. oris, Veillonella dispar or S. mutans did not cause any changes. The structure of the biofilm with regards to the localization of the species did not result in observable changes. In summary, the most striking observation of the present study was that absence of S. oralis resulted in limited growth of commensal A. oris and overgrowth of S. mutans. These data establish highlight S. oralis as commensal keeper of homeostasis in the biofilm by antagonizing S. mutans, so preventing a caries-favoring dysbiotic state.

Applications of the oral microbiome in personalized dentistry

“…However, recently, a number of oral streptococcal strains, such as Streptococcus dentisani (Lopez-Lopez, Camelo-Castillo, Ferrer, Simon-Soro, & Mira, 2017) and Streptococcus A12 (Huang et al, 2016) have been isolated from individuals with low caries experience; these strains can generate alkali from arginine and produce inhibitors against the cariogenic mutans streptococci, while being able to naturally colonize the mouth. Streptococcus oralis can also outcompete S. mutans when cultured together in multi-species biofilms (Thurnheer & Belibasakis, 2018). Hence, changes in the diversity and composition of the oral microbiome exposed to probiotics may help identify individuals, or populations, responsive to this application, or ones for which it may have negative or no effects in terms of oral health.…”

Isolation and Bacteriocin-Related Typing of Streptococcus dentisani

“…In the worst case, strain 7746 could out-compete a resident anti-cariogenic S. dentisani -like strain and then disappear due to failed adaptation to the host. It could also interfere with streptococcal strains and species that naturally keep homeostasis and antagonize S. mutans (Huang et al, 2018; Thurnheer and Belibasakis, 2018).…”

A Comparison of Flavorless Electronic Cigarette-Generated Aerosol and Conventional Cigarette Smoke on the Survival and Growth of Common Oral Commensal Streptococci

“…These species are considered commensal early colonizers [20,21,22]. All four species are beneficial to the host oral cavity in the context of their interactions with pathogenic species related both to caries and periodontal disease [23,24,25,26,27,28]. By extension, since oral health and overall general health are directly correlated, any disruption to the bacterial flora within the oral cavity could lead to systemic diseases, especially certain types of cardiovascular disease [29].…”