Capsaicin Shows Species and Strain-specific Activity: Investigation of the Antibacterial Effects on the Oral Pathogen Streptococcus mutans and the Oral Probiotics Streptococcus salivarius M18 and K12

Extensive research has investigated capsaicin (CAP), the primary bioactive compound in chili peppers, to explore its diverse pharmacological and physiological properties. Recently, the focus has shifted to understanding the potential effects of CAP on gut microbiota due to the strong link between gut bacterial profile and diet. However, there has been no research on the effects of CAP on oral microbiota. Therefore, our study aimed to explore the antibacterial effects of CAP on two oral probiotics, Streptococcus salivarius M18, and S. salivarius K12, along with the oral pathogen S. mutans. Previously, the anti-cancer activity of CAP had been demonstrated, and in accordance with these findings, here, we show its growth inhibitory activity on colorectal cancer cell lines. However, this study is the first to examine the impact of CAP on specific oral microorganisms while considering the oral consumption of CAP and the interconnectedness of the oral and gut microbiomes. The findings revealed that CAP exhibited antibacterial properties against the M18 strain at concentrations exceeding 100 µg/mL. Surprisingly, it did not show any growth-inhibitory effects on S. salivarius K12, even at a concentration of 2 mg/mL. Similarly, CAP did not inhibit the growth of S. mutans, a significant factor in dental caries. These results suggest that CAP's effects are species and strain-specific, indicating potential changes in the oral microbiota upon CAP consumption.