Antibacterial Effect of Oral Care Gel-Containing Hinokitiol and 4-isopropyl-3-methylphenol Against Intraoral Pathogenic Microorganisms

ObjectiveDeterioration of oral hygiene is closely related to increase severity and mortality of corona virus disease-19 (COVID-19), and also contribute to the development of various diseases such as aspiration pneumonia or Alzheimers. Oral care is attracting high interest in Japan, which has entered a super-aging society. In this study, we aimed to investigate whether commercially available Hinora(R) (HO) that oral care gels-containing hinokitiol and 4-isopropyl-3-methylphenol (IPMP) have biofilm formation inhibitory and antibacterial activities against various intraoral pathogen microorganisms. MethodCandida spp., Aggregatibacter actinomycetemcomitans, Staphylococcus aureus, and Pseudomonas aeruginosa were selected during the study period, all which were analyzed using antimicrobial disc, microorganism turbidity, and crystal violet assays. In addition, the germ tube test using C. albicans was performed with a modification of Mackenzies method. Images for morphological observation of the germ tubes were acquired with an inverted microscope. For comparison between products, we used Refrecare(R) (RC), which contains only hinokitiol (not containing IPMP). ResultsAll the intraoral pathogenic microorganisms showed drug susceptibility against undiluted form HO and/or RC. In particular, HO was more effective at lower concentrations than RC. In the HO-added group, inhibition circles were observed in all bacteria except P. aeruginosa when added at a concentration of 0.5 g/mL or more. The optical density values at 590 nm (crystal violet) and/or 600 nm (microorganism turbidity) of all the fungi and bacteria were significantly lower when cultured in medium with HO. Inhibition of growth or biofilm formation was observed when HO was added at a concentration of 0.05 g/mL or higher. To investigate the action mechanism of HO, germ tube tests were performed in C. albicans. The results show that culturing C. albicans in soyabean-casein digest broth with HO (0.05 g/mL) significantly suppressed germ tube formation. ConclusionsThese data suggest that oral care gel-containing hinokitiol and IPMP has strong biofilm formation inhibitory, antifungal and antibacterial effects against Candida fungi and multiple intraoral pathogenic microorganisms. Therefore, it may be a promising treatment option for oral infections.