Inhibitory Effects of 12 Major Citrus-Derived Monoterpenes on Streptococcus mutans

Background Monoterpenes, the main components of essential oils in citrus fruits, exhibit antibacterial activity against various bacteria. However, the specific inhibitory effects of individual monoterpenes on Streptococcus mutans , a key contributor to dental caries, remain unclear. This study identified major monoterpenes through a literature review and evaluated their inhibitory effects on S. mutans . Materials and methods A literature search using the keywords ‘citrus’, ‘terpene’, and ‘antimicrobial’ identified 12 representative monoterpenes from 277 articles. Filtrates were prepared by adding an excess amount of these monoterpenes and removing undissolved material via filtration. These monoterpene solutions were added to bacterial suspensions at volume fractions of 1/100 and 1/10, and analyses were conducted to examine their effects on the survival, growth, and biofilm formation of S. mutans . Results Among the 12 monoterpenes, three at a volume fraction of 1/100 and six at a volume fraction of 1/10 significantly reduced S. mutans cell numbers compared with controls ( P < .05). Five monoterpenes at a volume fraction of 1/100 and all 12 at a volume fraction of 1/10 significantly inhibited bacterial growth ( P < .01). Regarding biofilm formation, three monoterpenes at a volume fraction of 1/100 and four at a volume fraction of 1/10 exhibited significant inhibitory effects ( P < .05). Thymol consistently demonstrated significant inhibitory effects on survival, growth, and biofilm formation at both dilutions ( P < .05). Conclusion Many monoterpenes inhibited S. mutans survival, growth, and biofilm formation. Monoterpenes may hold promise as effective agents for preventing S. mutans -related dental caries.