Investigation of the antibacterial effects of hinokitiol on Lactobacillus casei

Abstract

Hinokitiol (HNK), which is known for its stress-relieving properties in living organisms and antimicrobial activity against both bacteria and fungi, has been used in oral care products such as bath additives, toothpaste, and mouthwash, as a form of aromatherapy. This study assessed the antibacterial effects of HNK on Lactobacillus casei (L. casei) isolates from patients with dental caries. L. casei was cultured on de Man, Rogosa and Sharpe (MRS) medium, for 24 h. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of HNK against L. casei were determined using the liquid dilution method. Furthermore, the bactericidal effect of HNK on L. casei was evaluated using adenosine triphosphate (ATP) bioluminescence and flow cytometry. The MIC and MBC for HNK against L. casei were determined to be 12.5 μg/mL and 50 μg/mL, respectively. In addition, when HNK solution was added to L. casei cultures adjusted to 106 CFU/mL at the MIC concentration, the ATP levels within the L. casei cells significantly decreased in the experimental group compared with the controls after 24 h. Moreover, staining with propidium iodide (PI) and fluorescence intensity measurements using flow cytometry revealed that the addition of HNK increased the number of dead cells. In summary, HNK demonstrated significant antibacterial effects against L. casei, suggesting its potential as a plant-derived agent for the prevention of dental caries. This study highlights the potential of HNK as a component of dental care for caries prevention. (J Osaka Dent Univ 2025; 59: 7-11)